BRYOPHYTA  , the botanical name of the second See also:

• GREAT

great sub-See also:

• DIVISION (from Lat. dividere, to break up into parts, separate)

division of the See also:

• VEGETABLE

vegetable See also:

• KINGDOM

kingdom, which includes the mosses and liverworts . They are all See also:

• PLANTS

plants of small, often See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute, See also:

• SIZE

size, and, as the See also:

• ABSENCE (Lat. absentia)

absence of popular names indicates, the different kinds are not commonly recognized . Even the distinction between liverworts and mosses is not clearly made, not only the former but other small plants of higher See also:

• GROUPS
• GROUPS, THEORY

groups being popularly called mosses . A little careful observation soon shows, however, that the Bryophytes See also:

• FORM (Lat. forma)

form a well-defined class, including several subordinate groups . Though their study necessarily involves minute observation they possess many features of See also:

• INTEREST

interest . The adaptations they show to their conditions of See also:

• LIFE

life are often very perfect and See also:

• PRESENT

present interesting analogies with the adaptive characters of the higher plants . They are of great scientific interest not only as representing a See also:

• SPECIAL

special type of life-See also:

• HISTORY

history and organization, but because in several of the subordinate groups See also:

• SERIES (a Latin word from serere, to join)

series of forms can be traced, which enable the See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general course, of their See also:

• EVOLUTION

evolution to be inferred even in the See also:

• PRACTICAL

practical absence of fossil remains of any antiquity . Bryophytes are very generally distributed over the See also:

• EARTH
• EARTH (a word common to Teutonic languages, cf. Ger. Erde, Dutch aarde, Swed. and Dan. jord; outside Teutonic it appears only in the Gr. 'pq'e, on the ground; it has been connected by some etymologists with the Aryan root ar-, to plough, which is seen in
• EARTH, FIGURE OF
• EARTH, FIGURE OF THE

earth, and those of a single See also:

• COUNTRY (from the Mid. Eng. contre or contrie, and O. Fr. cuntree; Late Lat. contrata, showing the derivation from contra, opposite, over against, thus the tract of land which fronts the sight, cf. Ger. Gegend, neighbourhood)

country, such as See also:

• BRITAIN (Gr. Hperavuml vi7vot, Bperravia; Lat. Britannia, rarely Britannia)

Britain, afford examples of all the See also:

• CHIEF (from Fr. chef, head, Lat. caput)

chief natural groups . Sometimes, as is the See also:

• CASE
• CASE, JOHN (d. 1600)

case with the See also:

• BOG (from Ir. and Gael. bogach, bog, soft)

bog-mosses and some See also:

• ARCTIC (Gr. "ApKroc, the Bear, the northern constellation of Ursa Major)

arctic mosses, they may See also:

• COVER (from the Fr. convert, from couvrir, to cover, Lat. cooperire)

cover considerable tracts . As a See also:

• RULE

rule, however, they occupy a subordinate See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place in the vegetation, and the different kinds require to be carefully looked for . Covering, as they often do, what would otherwise be See also:

• BARE

bare ground, they are of value in assisting to retain moisture in the See also:

• SOIL

soil and in preparing the way for its colonization by higher plants . Although many forms are capable of withstanding periods of drought they succeed best in relatively moist climates and localities .

This is shown both by their unequal abundance in different localities of one country and in their scarcity in certain See also:

• GEOGRAPHICAL

geographical regions as compared with their luxuriance in others . The See also:

• EXTERNAL

external See also:

• APPEARANCE (from Lat. apparere, to appear)

appearance and general organization show great variety . In all mosses and many liverworts (See also:

• FIGS

figs . 8, 11) the plant consists of a See also:

• STEM (O. Eng. staefn, stemn, cf. Du. stain, Ger. Stamm, &c., probably related to " staff ")

stem bearing small leaves . In a number of liverworts (figs . 2, 7), on the other See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

hand, it presents no distinction of stem and See also:

• LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

leaf, but is a See also:

• FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

flat, See also:

• DORSIVENTRAL (Lat. dorsum, the back, venter, the belly)

dorsiventral See also:

• BODY

body usually closely applied to the substratum on which it grows . This, in contradistinction to the leafy shoot, is termed a thallus . True roots are never present, the plants being attached to the soil by rhizoids, which resemble the See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root-hairs of higher plants . The reproductive See also:

• ORGANS

organs See also:

• BORNE, KARL LUDWIG (1786–1837)

borne by the thallus or plant are called antheridia and archegonia, and serve for sexual See also:

• REPRODUCTION

reproduction . The antheridium (figs . 5, 15) has a longer or shorter stalk and consists of a See also:

• WALL (O. Eng. weal, weall, Mid. Eng. wal, wane, adapted from Lat. vallum, rampart; the original O. Eng. word for a wall was wag or tenth)
• WALL, RICHARD (1694-1778)

wall formed of a single layer of flat cells enclosing a See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass of minute cells from which the spermatozoids are See also:

• DEVELOPED

developed . In the cases which have been most carefully investigated two spermatozoids have been found to arise from each of the small cubical cells of the central See also:

• TISSUE (Fr. tissu, tissue, participle of tisser, Lat. texere, to weave)

tissue .

When mature the antheridium opens on being moistened and the spermatozoids become See also:

• FREE

free in the See also:

• WATER

water by the See also:

• DISSOLUTION (from Lat. dissolvere, to break up into parts)

dissolution of the mucilaginous See also:

• CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell-walls enclosing them . Each has the form (fig . 5, D) of a more or less spirally See also:

• TWISTED

twisted, See also:

• CLUB (connected with " clump ")

club-shaped body, bearing at the pointed anterior end two See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long See also:

• CILIA (plural of Lat. cilium, eyelash)

cilia by means of which it moves through the water . The archegonium (fig. i) has 1 . Mature but unopened arche- down to the rounded gonium. e, Ovum ; b, ven- ovum e . tral-See also:

• CANAL
• CANAL (from Lat. canalis, " channel " and " kennel " being doublets of the word)

canal cell; d, lid-cells of 3 . Archegonium after fertilizaneck, tion; the fertilized ovum is 2 . Archegonium ready for fer- developing into a sporo- tilization; a passage leads gonium f; d, perianth . the form of a narrow See also:

• FLASK

flask with a long See also:

• NECK (O. Eng. hnecca; the word appears in many Teutonic languages; cf. Dutch ride, Ger. Nacken; in O. E. the common word was heals; cf. Ger. Hals)

neck . It usually has a See also:

• SHORT, FRANCIS JOB (1857– )

short stalk and consists of a central See also:

• ROW, JOHN (c. 1525—1580)

row of cells enclosed by a layer of cells forming the wall . The See also:

• EGG (O.E. aeg, cf. Ger. Ei, Swed. aegg, and prob. Gr. u,ov, Lat. ovum)
• EGG, AUGUSTUS LEOPOLD (1816-1863)

egg-cell or ovum lies within the wider basal region or venter, and above it come the ventral canal-cell and canal-cells within the neck of the archegonium . When the archegonium opens by the separation of the cells at the tip, the disorganized canal-cells See also:

• ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

escape, leaving a narrow tubular passage leading down to the ovum .

Each antheridium or archegonium arises from a single cell, and while the mature structure is similar in the two groups, the development presents See also:

• DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

differences in liverworts and mosses . Without entering into details it may be mentioned that in the mosses it proceeds both in the archegonium and antheridium by the segmentation of an apical cell, while this is not the case in the See also:

• LIVER (O. Eng. lifer; cf. cognate forms, Dutch lever, Ger. Leber, Swed. lefver, &c.; the O. H. Ger. forms are libara, lipora, &c.; the Teut. word has been connected with Gr. i'prap and Lat. jecur)

liver-worts . Fertilization is effected by the passage of a spermatozoid, attracted probably by means of a chemical stimulus, down the passage of the archegonial neck and its See also:

• FUSION

fusion with the ovum . It thus, as in other cases of sexual reproduction, involves the See also:

• UNION
• UNION (known locally as Union Hill and officially as Town of Union)

union of two cells, and the vegetative plant; since it bears the sexual organs, is called the sexual See also:

• GENERATION (from Lat. generare, to beget, procreate; genus, stock, race)

generation or gametophyte . From the fertilized ovum another and very different See also:

• STAGE (Fr. 6/age; from Lat. stare, to stand)

stage arises, which remains attached to the sexual plant and has thus the appearance of a See also:

• FRUIT (through the French from the Lat. fructus; frui, to enjoy)

fruit borne on it . It consists of a See also:

• CAPSULE (from the Lat. capsula, a small box)

capsule usually borne on a longer or shorter stalk or seta, the See also:

• BASE

base of which is inserted into the tissues of the gametophyte . This basal region, which serves to absorb nourishment, is called the See also:

• FOOT

foot . Within the capsule numerous reproductive cells, the spores, are developed . In contrast to the sexual generation this stage is called the spore-bearing generation (sporogonium, sporophyte) . The examination of any See also:

• MOSS

moss" in fruit " (fig . II, B) will show the readily detachable sporogonium borne on the leafy sexual plant, and the relation existing between the two generations will be evident from figs . 2, 3, 9, and 16 .

In liverworts (with one or two exceptions) the mature capsule is filled with spores mingled with sterile cells or elaters and opens by splitting into valves . In mosses (fig . 11, C) the sporogonium is more highly organized; a central See also:

• COLUMN (Lat. columna)

column of sterile tissue (the See also:

• COLUMELLA, LUCIUS JUNIUS MODERATUS

columella) is found in the capsule, which opens by the removal of a lid or operculum, and there are no elaters among the spores . By the opening of the capsule the spores are set free, and under suitable conditions germinate and give rise to the sexual generation . In mosses (fig . 12) a filamentous growth, the protonema, is first formed, and the leafy plants arise upon this . In liverworts this preliminary phase of the sexual generation is as a rule See also:

• ILL

ill-marked or absent, and the plant may be said to develop directly from the spore . It will be evident that the two generations exhibit a See also:

• REGULAR

regular See also:

• SUCCESSION (Lat. successio, from succedere, to follow after)

succession or See also:

• ALTERNATION (from Lat. alternare, to do by turns)

alternation in the life-history of all Bryophytes . The gametophyte is developed from the spore and bears the sexual organs; the sporogonium is developed from the fertilized egg and produces spores . An important cytological difference between the two generations can only be mentioned here . By the union of the nuclei of the spermatozoid and ovum in fertilization the number of chromosomes in the resulting See also:

• NUCLEUS (Lat. for the kernal of a nut, nux, the stone of fruit)

nucleus is doubled, and this See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)

double number is maintained throughout all the cell-divisions of the sporogonium . On the development of the spores, which takes place by the division of each spore-See also:

• MOTHER

mother-cell into four, the number of chromosomes becomes one See also:

• HALF

half of what it has been in all the nuclei of the sporogonium .

This reduced number is maintained throughout the development of the sexual generation . Thus in Pellia the nuclei of the gametophyte have eight chromosomes and those of the sporophyte sixteen . The relation in which the two generations stand to one another is the most important See also:

• COMMON

common characteristic of the Bryophyta . The gametophyte is always the independently living individual upon which the spore-bearing generation is through-out its life dependent . In all plants higher than the Bryophyta the sporophyte becomes an independently rooted plant and is the conspicuous stage in the life-history . Thus in the See also:

• FERN (from O. Eng. fearn, a word common to Teutonic languages, cf. Dutch varen, and Ger. Farn; the Indo-European root, seen in the Sanskrit parna, a feather, shows the primary meaning; cf. Gr. rmep6 , feather, rTepis, fern)

fern the sexual generation is the small prothallus developed from the spore, while the See also:

• FAMILIAR (through the Fr. familier, from Lat. familiaris, of or belonging to the familia, family)

familiar fern-plant is the spore-bearing generation (see PTExIno-PHYTA) . On the other hand a corresponding alternation of generations is only indicated in the See also:

• LOWER

lower plants (Thallophyta) . The Bryophyta are divided into the Hepaticae (liverworts) and Musci (mosses) . In the Hepaticae we can recognize three subordinate groups—the Marchantiales, Jungermanniales and Anthocerotales; and in the Musci also three groups—the Sphagnales, Andreaeales and Bryales . Since these series of forms differ considerably among themselves, it is difficult to See also:

• EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express in a See also:

• DEFINITION (Lat. definitio, from de-finire, to set limits to, describe)

definition the distinction between a liverwort and a moss which is readily made in practice . We may therefore leave it to the description of the several groups of Hepaticae and Musci to supplement the differences mentioned above and to bring out the exceptions which exist . Hepaticas (Liverworts) .

The range of form and structure of both generations in the liverworts is so great that no one form can be taken as a satisfactory type . It will, however, be of use to See also:

• PREFACE (Med. Lat. prefatia, for classical praefatio, praefari, to speak beforehand)

preface the more general description by a brief See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account of a particular example, and we may take for this purpose a very common and easily recognized thalloid liverwort belonging to the Jungermanniales . Pellia epiphylla (fig . 2) can be found at any See also:

• SEASON (0. Fr. seson, seison, mod. saison, Lat. satio, sowing time, the spring, from serere, to sow; in Late Lat. the word is found with its present meaning, the spring being considered as particularly the season of the year)

season growing in large patches on the See also:

• DAMP

damp soil of See also:

• WOODS, LEONARD (1774-1854)
• WOODS, SIR ALBERT (1816-1904)

woods, See also:

• BANKS, GEORGE LINNAEUS (1821-1881)
• BANKS, NATHANIEL PRENTISS (1816–1894)
• BANKS, SIR JOSEPH
• BANKS, THOMAS (1735-1805)

banks, &c . The broad flat thallus is See also:

• GREEN, A
• GREEN, ALEXANDER HENRY (1832—1896)
• GREEN, DUFF (1791—1875)
• GREEN, JOHN RICHARD (1837—1883)
• GREEN, MATTHEW (1696-1737)
• GREEN, THOMAS HILL (1836-1882)
• GREEN, VALENTINE (1739–1813)
• GREEN, WILLIAM HENRY (.1825–1900)

green and may be a couple of inches long . It is sparingly branched, the branching being apparently dichotomous; the growing point is situated in a depression at the anterior end of each See also:

• BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch . The wing-like lateral portions of the thallus gradually thin out from the midrib; from the projecting lower See also:

• SURFACE

surface of this numerous rhizoids See also:

• SPRING (from " to spring," " to leap or jump up," " burst out," O. Eng., springau, a common Teut. word, cf. Ger. springer, possibly allied to Gr. QnrFpxecOac, to move rapidly)

spring . These are elongated superficial cells, and serve to See also:

• FIX, THEODORE (180o-1846)

fix the thallus to the soil and obtain water and salts from it . No leaf-likeappendages are borne on the thallus, but short glandular hairs occur behind the See also:

• APEX

apex . The plant is composed throughout of very similar living cells, the more superficial ones containing numerous See also:

• CHLOROPHYLL (from Gr. XAwpos, green, 4bXXov, a leaf)

chlorophyll grains, while See also:

• STARCH

starch is stored in the See also:

• INTERNAL

internal cells of the midrib . The cells contain a number of oil-bodies the See also:

• FUNCTION

function of which is imperfectly understood . The growth of the thallus proceeds by the regular segmentation of a single apical cell .

The sexual organs are borne on the upper surface, and both antheridia and archegonia occur on the same branch (fig . 3, A) . The antheridia (an) are scattered over the See also:

• MIDDLE

middle region of the thallus, and each is surrounded by a tubular upgrowth from the surface . The archegonia (ar) are developed in a See also:

• GROUP

group behind the apex, and the latter continues to grow for a See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time after their formation, so that they come to be seated in a depression of the upper surface . They are further protected by the growth of the hinder margin of the depression to form a See also:

• SCALE
• SCALE (1) A

scale-like involucre (in) . Fertilization takes place about See also:

• JUNE

June, and the sporogonium is fully developed by the See also:

• WINTER, JOHN STRANGE
• WINTER, PETER (c. 1755-1825)

winter . The embryo developed from the fertilized ovum consists at first of a number of tiers of cells . Its terminal tier gives rise to the capsule, the first divisions in the four cells of the tier marking off the wall of the capsule from the cells destined to produce the spores . In fig: 4, C, which represents a See also:

• LONGITUDINAL

longitudinal See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section of a See also:

• YOUNG
• YOUNG, A
• YOUNG, ARTHUR (1741-1820)
• YOUNG, BRIGHAM (1801-1877)
• YOUNG, CHARLES MAYNE (1777–1856)
• YOUNG, EDWARD (1683–1765)
• YOUNG, JAMES (1811-1883)
• YOUNG, THOMAS (1773-1829)

young embryo of Pellia, these archesporial cells are shaded . The tiers below give rise to the seta and foot . The mature sporogonium (fig . 3, B) consists of the foot embedded in the tissue of the thallus, the seta, which remains short until just before the shedding of the spores, and the spherical capsule .

It remains for long enclosed within the calyptra formed by the further development of the archegonial wall and surmounted by the neck of the archegonium . The calyptra is ultimately burst through, and in See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

early spring the seta elongates rapidly, raising the dark-coloured capsule (fig . 2) . In the young See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition the wall of the capsule, which consists of two layers of cells, encloses a mass of similar cells developed from the archesporium . Some of these become spore-mother-cells and give rise by cell division to four spores, while others remain undivided and become the elaters . The latter are elongated spindle-shaped A, Longitudinal section of thallus mature sporogonium at- at the time of fertilization. tached to the thallus. in, an, Antheridia; ar, arche- Involucre; cal, calyptra; gonia; in, involucre. f, foot; s, seta; caps, cap- B, Longitudinal section of almost sule (semi-diagrammatic) . cells with thick See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

brown See also:

• SPIRAL

spiral bands on the inside of their thin walls . They radiate out from a small plug of sterile cells projecting into the base of the capsule, and some are attached to this, while others See also:

• LIE, JONAS LAURITZ EDEMIL (1833—1908)
• LIE, MARIUS SOPHUS (1842–1899)

lie free among the spores . The latter are large, and at first are unicellular; but in Pellia, which in this respect is exceptional, they commence their further development within the capsule, and thus consist of several cells when See also:

• SHED

shed . caps From See also:

• COOKE, GEORGE FREDERICK (1756–1811)
• COOKE, JAY (1821–1905)
• COOKE, ROSE TERRY (1827-1892)

Cooke, Handbook of Britiet . Hepatuae . The cells of the capsule wall have incomplete, brown, thickened rings on their walls, and the capsule opens by splitting into four valves, which See also:

• BEND

bend away from one another, allowing the loose spores to be readily dispersed by the See also:

• WIND
• WIND (a common Teut. word, cognate with Skt. vats, Lat. ventus, cf. " weather," to be of course distinguished from to " wind," to coil or twist, O.Eng. windan, cf. "wander," "wend," &c.)

wind, assisted by the hygroscopic movements of the elaters .

On falling upon damp soil the spores germinate, growing into a thallus, which gradually attains its full size and bears sexual organs . While the general course of the life-history of all liverworts re- sembles that of Pellia, the three great groups into which they are divided differ from one another in the characters of both genera- tions . Each group exhibits a series leading from more See also:

• SIMPLE

simple to more highly organizedforms,andthe differentiation has proceeded on distinct and to some extent divergent lines in the three groups . The Marchantiales are a series of thalloid forms, in which the structure of the thallus is specialized to enable them to live in more exposed situations . The lowest members of the series (Riccia) possess the simplest sporogonia known, consisting of a wall of one layer of cells enclosing the spores . In the higher forms a sterile foot and seta is present, and sterile cells or elaters occur with the spores . The lower members of the Jungermanniales are also thalloid, but the thallus never has the complicated structure characteristic of theMarchantiales,and progress is in the direction of the differentiation of the plant into stem and leaf . Indications of how this may have come about are afforded by the lower group of the Anacrogynous Jun- germanniaceae, and throughout the Acrogynous Junger- manniacae the plant has well- marked stem and leaves . The sporo- gonium even in the simplest forms has a sterile foot, but in this series also the origin of elaters from sterile cells can be traced . The Anthocerotales are a small and very distinct group, in which the gameto- phyte is a thallus, while the sporo- gonium possesses a sterile columella and is capable of long-continued growth and spore See also:

• PRODUCTION (Lat. productionem, from producere, to pro-duce)

production . The mode of development of the sporogonium presents important differences in the three series that may be briefly referred to here . In fig .

4 young sporogonia of a number of liverworts are shown in longitudinal section, and the archesporial cells from which the spores and elaters will arise are shaded . In Riccia (fig . 4, A) the whole mass of cells derived from the ovum forms a spherical capsule, the only sterile tissue being the single layer of peripheral cells forming the wall . In other Marchantiales (fig . 4, B) the lower half of the embryo separated by the first transverse wall (1, I) forms the sterile foot and seta, while in the upper half (ka) the peripheral layer forms the wall of the capsule, enclosing the archesporial cells from which spores and elaters arise . In the Jungermanniales (fig . 4, C, E, F) the embryo is formed of a number of tiers of cells, and the archesporium is defined by the first divisions parallel to the surface in the cells of one or more of the upper tiers; a number of tiers go to form the seta and foot, while the lowest segment (a) usually forms a small appendage of the latter . In the Anthocerotales (fig . 4, D) the lowest tiers form the foot, and the terminal tier the capsule . The first periclinal divisions in the cells of the terminal tier See also:

• SEPARATE

separate a central group of cells which form the sterile columella (See also:

• COL
• COL (Fr. for " neck," Lat. collum)

col) . The archesporium arises by the next divisions in the See also:

• OUTER

outer layer of cells, and thus extends over the See also:

• SUMMIT

summit of the columella . In none of the liverworts does the sporogonium develop by means of an apical cell, as is the rule in mosses .

Leaving details of form and structure to be considered under the several groups, some general features of the Hepaticae may be looked at here in relation to the conditions under which the plants live . The organization of the gametophyte stands in the closest relation to the factors of See also:

• LIGHT

light and moisture in the environment . With hardly an exception the liverworts are dorsiventral, and usually one See also:

• SIDE
• SIDE (mod. Eski Adalia)

side is turned to the substratum and the other exposed to the light . In thalloid forms a thinner marginal expansion or a definite wing increasing the surface exposed to the light can be distinguished' from a thicker midrib serving for storage and See also:

• CONDUCTION, ELECTRIC

conduction . The leaves and stem of the foliose forms effect the same division of labour in another way . The relation of the plant to its water See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply varies within the group . In the Marchantiales the chief supply is obtained from the soil by the rhizoids, and its loss in transpiration is regulated and controlled . In most liver-worts, on the other hand, water is absorbed directly by the whole general surface, and the rhizoids are of subordinate importance . Many forms only succeed in a constantly humid See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere, while others sustain drying for a See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period, though their See also:

• POWERS, HIRAM (1805-1873)

powers of assimilation and growth are suspended in the dry See also:

• STATE
• STATE, GREAT OFFICERS OF

state . The cell-walls are capable of imbibing water rapidly, and their thickness stands in relation to this rather than to the prevention of loss of water from the plant . The large surface presented by the leafy forms facilitates the retention and absorption of water . The importance of prolonging the moistened condition as long as possible is further shown by special adaptations to retain water either between the appressed lobes of the leaves or in special See also:

• PITCHER

pitcher-like sacs .

In thalloid forms See also:

• FIMBRIATE (from Lat. fimbriae, fringe)

fimbriate or lobed margins or outgrowths from the surface See also:

• LEAD
• LEAD (pronounced iced)

lead to the same result . Sometimes adaptations to protect the plant during seasons of drought, such as the See also:

• ROLLING

rolling up of the thallus in many xerophytic Marchantiales, can be recognized, but more often a prolonged dry season is survived in some resting state . The formation of subterranean tubers, which persist when the See also:

• REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest of the plant is killed by drought, is an interesting See also:

• ADAPTATION (from Lat. adaptare. to fit to)

adaptation to this end, and is found in all three groups (e.g. in See also:

• SPECIES

species of Riccia, Fossombronia and Anthoceros) . No examples of See also:

• TOTAL

total saprophytism or of See also:

• PARASITISM

parasitism are known, but two interesting cases of a symbiosis with other organisms which is probably a mutually beneficial one, though the nature of the physiological relation between the organisms is not clearly established, may be mentioned . Fungal hyphae occur in the rhizoids and in the cells of the lower region of the thallus of many liverworts, as in the endotrophic mycorhiza of higher plants . Colonies of Nostoc are constantly found in the Anthocerotaceae and in Blasia . In the latter they are protected by special See also:

• CONCAVE

concave scales, while in the Anthocerotaceae they occupy some of the See also:

• MUCILAGE (from Late Lat. mucilago, a mouldy juice, from mucere, to be mouldy)

mucilage slits between the cells of the lower surface of the thallus . Other adaptations concern the See also:

• PROTECTION

protection of the sexual organs and sporogonia, and the retention of water in the neighbourhood of the archegonia to enable the spermatozoid to reach the ovum . In thalloid forms the sexual organs are often sunk in depressions, while in the foliose forms protection is afforded by the surrounding leaves . In addition special involucres around the archegonia have arisen independently in several series . The characters of the sporogonium have as their See also:

• OBJECT

object the See also:

• NUTRITION

nutrition and effective See also:

• DISTRIBUTION (Lat. distribuere, to deal out)

distribution of the spores, and only exceptionally, as in the Anthocerotaceae, are concerned with See also:

• INDEPENDENT

independent assimilation . In most forms the capsule is raised above the general surface at the time of opening, usually by the rapid growth of the seta, but in the Marchantiaceae by the sporogonia being raised on a special archegoniophore .

The elaters serve as lines of conduction of plastic material to the developing spores, and later usually assist in their dispersal . The spores, with few exceptions, are unicellular when shed, and may develop at once or after a resting period . In their germination a short filament of a few cells is usually developed, and the apical cell of the plant is established in the terminal cell . In other cases a small See also:

• PLATE

plate or mass of cells is formed . With one or two exceptions, however, this preliminary F A, Riccia . B, Marchantia poly- mor pha . C, Pellia epiphylla . D, Anthoceros laevis . E, Cephalozia bicuspidala . F, Radula complanala . phase, which may be compared with the protonema of mosses, is of short duration . The See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power of vegetative See also:

• PROPAGATION

propagation is widely spread .

When artificially divided small fragments of the gametophyte are found to be capable of growing into new individuals . Apart from the separation of branches by the decay of older portions, special gemmae are found in many species . In Aneura the contents of superficial cells, after becoming surrounded by a new wall and dividing, escape as bi-cellular gemmae . Usually the gemmae arise by the outgrowth of superficial cells, and become free by breaking away from their stalk . When separated they may be single cells or consist of two or numerous cells . In Blasia and Marchantia the gemma e are formed within tubular or See also:

• CUP (in O.E. cuppe; generally taken to be from Late Lat. cuppa, a variant of Lat. cupa, a cask, cf. Gr. KuaeXXov)

cup-shaped receptacles, out of which they are forced by the swelling of mucilage secreted by special hairs . Marchantiales.—The plants of this group are most abundant in warm sunny localities, and grow for the most See also:

• PART

part on soil or rocks often in exposed situations . Nine genera are represented in Britain . Targionia is found on exposed rocks, but the other forms are less strikingly xerophytic; Marchantia, polymorpha and Lunularia spread largely by the gemmae formed in the special gemma-cups on the thallus, and occur commonly in greenhouses . The large thallus of Conocephalus covers stones by the waterside, while Dumortiera is a hygrophyte confined to damp and shady situations . Among the Ricciaceae, most of which grow on soil, Ricciocarpus and Riccia natans occur floating on still water . The dorsiventral thallus is constructed on the same See also:

• PLAN
• PLAN (from Lat. planes, flat)

plan throughout the group, and shows a lower region composed of cells containing little chlorophyll and an upper stratum specialized for assimilation and transpiration .

The lower region usually forms a more or less clearly marked midrib, and consists of parenchymatous cells, some of which may contain oil-bodies or be differentiated as mucilage cells or sclerenchyma See also:

• FIBRES
• FIBRES (or FIBERS, in American spelling; from Lat. fibra, apparently connected either with filum, thread, or findere, to split)

fibres . Behind the apex, which has a number of initial cells, a series of amphigastria or ventral scales is formed . These consist of a single layer of cells, and their terminal appendages often See also:

• FOLD

fold over the apex and protect it . Usually they stand in two rows, but sometimes See also:

• ACCESSORY

accessory rows occur, and in Riccia only a single median row is present . The thallus bears two sorts of rhizoids, wider ones with smooth walls which grow directly down into the soil, and longer, narrower ones, with peg-like thickenings of the wall projecting into the cell-cavity . The peg-rhizoids, which are See also:

• PECULIAR

peculiar to the group, converge under shelter of the amphigastria to the midrib, beileath which they form a See also:

• WICK

wick-like strand . Through this water is conducted by capillarity as well as in the cell cavities . The upper stratum of the thallus is constructed to regulate the giving off of the water thus absorbed . It consists of a series of See also:

• AIR (from an Indo-European root meaning " breathe," " blow ")
• AIR, or ASBEN

air-See also:

• CHAMBERS (the Fr. chambre, from Lat. camera, a room)
• CHAMBERS, EPHRAIM (d. 1740)
• CHAMBERS, GEORGE (1803-1840)
• CHAMBERS, ROBERT (18oz-1871)
• CHAMBERS, SIR WILLIAM (1726-1796)

chambers (fig . 6, B) formed by certain lines of the superficial cells growing up from the surface, and as the thallus increases in See also:

• AREA

area continuing to See also:

• DIVIDE

divide so as to roof in the chamber . The layer forming the roof is called the " epidermis," and the small opening See also:

• LEFT

left leading into the chamber is bounded by a special See also:

• RING (O.E. hring; a word common to Teutonic languages; and probably cognate with the Lat. circus, Gr. KtpKOS or KpLKOS, Skt'. chakra, wheel, circle, cf. also " harangue "); in art, a band of circular shape of varying sizes, made of any material and used f

ring of cells and forms the " stoma " or air-See also:

• PORE

pore . In most species of Riccia the air-chambers are only narrow passages, but in the other Marchantiales they are more extended .

In the A . Portion of thallus (t) bearing surface (o); b, scales; It, twostalkedantheridiophores rhizoids . (hu) . C . Longitudinalsectionof anther- B . Longitudinal section through idium; st, stalk; w, a young antheridiophore. wall . The antheridia (a) are seated D . Two spermatozoids. in depressions of the upper simplest cases the sides and base of the chambers perform the See also:

• WORK

work of assimilation (e.g . Corsinia) . Usually the surface is extended by the development of partitions in the chambers (Reboulia), or by the growth from the See also:

• FLOOR (from O. Eng. flor, a word common to many Teutonic languages, cf. Dutch vloer, and Ger. Flur, a field, in the feminine, and a floor, masculine)

floor of the chamber of short filaments of chlorophyllous cells (Targionia . Marchantia, fig . 6) .

The stomata may be simply surrounded by one or more series of narrower cells, or, as in the thallus of Marchantia and on the archegoniophores of other forms, may become See also:

• BARREL (a word of uncertain origin common to Romance languages; the Celtic forms, as in the Gaelic baraill, are derived from the English)

barrel-shaped structures by the division of the ring of cells bounding the pore . In some cases the lowermost circle of cells can be approximated so as to See also:

• CLOSE
• CLOSE (from Lat. clausum, shut)
• CLOSE, MAXWELL HENRY (1822-1903)

close the pore . In Dumortiera the air-chambers are absent, their formation being only indicated at the apex . The sexual organs are always situated on the morphologically upper surface of the thallus . In Riccia they are scattered singly and protected by the air-chamber layer . The scattered position of the antheridia is also found in some of the higher forms, but usually they are grouped on special antheridiophores which in Marchantia are stalked, disk-shaped branch-systems (fig . 5) . The individual antheridia are sunk in depressions from which the spermatozoids are in some cases forcibly ejected . The archegonial groups in Corsinia are sunk in a depression of the upper surface, while in Targionia they are displaced to the lower side of the anterior end of a branch . In all the other forms they are borne on special archegoniophores which have the form of a disk-shaped See also:

• HEAD (in 0. Eng. heafad; the word is common to Teutonic languages; cf. Dutch hoofd, Ger. Haupt, generally taken to be in origin connected with Lat. caput, Gr. KerbOvi7)
• HEAD, SIR EDMUND WALKER, BART
• HEAD, SIR FRANCIS BOND, BART

head borne on a stalk . The archegoniophore may be an upgrowth from the dorsal surface of the thallus (e.g . Plagiochasma), or the apex of the branch may take part in its formation .

When the disk, around which archegonia are developed at intervals, is simply raised on a stalk-like continuation of the branch, a single groove protecting a strand of peg-rhizoids is found on the ventral See also:

• FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face of the stalk (Reboulia) . In the highest forms (e.g . Marchantia) the archegoniophore corresponds to the repeatedly branched continuation of the thallus, and the archegonia arise in relation to the growing points which are displaced to the lower surface of the disk . In this case two grooves are found in the stalk . The archegonia are protected by being sunk in depressions of the disk or by a special two-lipped involucre . In Marchantia and Fimbriaria an additional investment termed in descriptive See also:

• WORKS

works the perianth, grows up around each fertilized archegonium (fig. r, 3, d) . The simple sporogonium found in the Ricciaceae (fig . 4, A) has been described above; as the spores develop, the wall of the spherical capsule is absorbed and the spores lie free in the calyptra, by the decay of which they are set free . In Corsinia the capsule has a well-developed foot, but the sterile cells found among the spore-mother-cells do not become elaters, but remain thin-walled and simply contribute to the nutrition of the spores . In all other forms elaters with spirally thickened walls are found . The seta is short, the capsule being usually raised upon the archegoniophore . Dehiscence takes place either by the upper portion of the capsule splitting into short See also:

• TEETH (O.E. Eel); plural of tooth, O.E. top)

teeth or falling away as a whole or in fragments as a sort of operculum .

The spores on germination form a short germ-See also:

• TUBE (Lat. tuba)

tube, in the terminal cell of which the apical cell is established, but the direction of growth of the young thallus is usually not in the same straight See also:

• LINE

line as the germ-tube . The Marchantiales are divided into a number of groups which represent distinct lines of advance from forms like the Ricciaceae, but the details of their See also:

• CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification cannot be entered upon here . The general nature of the progression exhibited by the group as a whole will, however, be evident from the above account . Jungermanniales.—This large series of liverworts, which presents great variety in the organization of the sexual generation, is divided into two See also:

• MAIN (from the Aryan root which appears in " may " and " might," and Lat. magnus, great)
• MAIN (Lat. Moenus)

main groups according to whether the formation of archegonia terminates the growth of the branch or does not utilize the apex . The latter condition is characteristic of the more See also:

• PRIMITIVE

primitive group of the Anacrogynous Jungermanniaceae, in which the branch continues its growth after the formation of archegonia so that they (and later the sporogonia) stand on the dorsal surface of the thallus or leafy plant . In the Acrogynous Jungermanniacele the plant is throughout foliose, and the archegonia occupy the ends of the main shoot or of its branches . The antheridia are usually globular and long-stalked . The capsule opens by splitting into four halves . Jungermanniaceae Anacrogynae.—The great range of form in the sexual plant is well illustrated by the nine genera of this group A From Strasburger's See also:

• TEXT (Lat. textum, woven fabric, from texere, to weave)

Text-See also:

• BOOK

book of See also:

• BOTANY (from Gr. l3or6v17, plant; ,66vicety, to graze)

Botany . 704 which occur in Britain . One thalloid form has already been described in Pellia (fig . 2) .

Sphaerocarpus, which occurs rarely in stubble See also:

• FIELDS, JAMES THOMAS (1817-1881)

fields, is in many respects one of the simplest of the liverworts . The small thallus bears the antheridia and archegonia, each of which is surrounded by a tubular involucre, on the upper surface of distinct individuals . The sporogonium has a small foot, but the sterile cells among the spores do not develop into elaters . The same is true of the capsule of Riella . The plants of this genus, none of the species of which are See also:

• BRITISH

British, grow in shallow water rooted in the mud, and are unlike all other liverworts in appearance . The usually erect thallus has a broad wing-like outgrowth from the dorsal surface and two rows of rather large scales below . No See also:

• PROVISION (Lat. provisio)

provision for the opening of the capsule exists in either of these genera . In Aneura the form of the plant may be complicated by a division of labour between root-like, stem-like and assimilating branches of the thallus . The sexual organs are borne on short lateral branches, while in the related genus Metzgeria, which occurs on rocks and See also:

• TREE (0. Eng. treo, treow, cf. Dan. tree, Swed. Odd, tree, trd, timber; allied forms are found in Russ. drevo, Gr. opus, oak, and 36pv, spear, Welsh derw, Irish darog, oak, and Skr. dare, wood)
• TREE, SIR HERBERT BEERBOHM (1853- )

tree trunks, the small sexual branches spring from the lower surface of the midrib of the narrow thallus . In these two genera the elaters are attached to a sterile group of cells projecting into the upper'end of the'capsule, and on dehiscence remain connected with the tips of the valves . Pallavicinia and some related genera have a definite midrib and broad wings formed of one layer of cells, and are of interest owing to the presence of a special water-conducting strand in the midrib . This consists of elongated lignified cells with pitted walls .

Blasia pusilla, which occurs commonly by ditches and streams, affords a transition to the foliose types . Its thallus (fig . 7) has thin marginal lobes of limited growth, which are comparable to the more definite leaves of other anacrogynous forms . The ventral surface bears flat scales in addition to the concave scales which, as mentioned above, are inhabited by Nostoc . This interesting liverwort produces two kinds of gemmae, and in the localities in which it grows is largely reproduced by their means . In Fossombronia, of which there are a number of British species, the plant consists of a flattened stem creeping on muddy soil and bearing two rows of large obliquely-placed leaves . The sexual organs are borne on the upper surface of the midrib, and the sporogonium is surrounded by a See also:

• BELL
• BELL, ALEXANDER MELVILLE (1819—1905)
• BELL, ANDREW (1753—1832)
• BELL, GEORGE JOSEPH (1770-1843)
• BELL, HENRY (1767-1830)
• BELL, HENRY GLASSFORD (1803-1874)
• BELL, JACOB (1810-1859)
• BELL, JOHN (1691-178o)
• BELL, JOHN (1763-1820)
• BELL, JOHN (1797-1869)
• BELL, ROBERT (1800-1867)
• BELL, SIR CHARLES (1774—1842)

bell-shaped involucre which grows up after fertilization . Treubia, which grows on rotting See also:

• WOOD, ANTHONY A2 (1632-1695)
• WOOD, JOHN GEORGE (1827—1889)
• WOOD, MRS HENRY [ELLEN] (1814—1887)
• WOOD, SEARLES VALENTINE (1798—188o)

wood in the See also:

• MOUNTAIN (0. Fr. montaigne; popular Lat. montanea, an adjectival form from the classical mons, montis, whence Eng. " mount," a form usually used along with the name of an individual mountain, e.g. Mt Everest)
• MOUNTAIN, THE (La Montagne)

mountain forests of See also:

• JAVA

Java, is similarly differentiated into stem and leaf, and is the largest liverwort known, reaching a length of See also:

• THIRTY

thirty centimetres . Lastly Haplomitrium, a rare British genus, forms with the See also:

• EXOTIC (Gr. EWTIK6s, foreign, from few, outside)

exotic Calobryum, an isolated group which is most naturally placed among the anacrogynous forms although the archegonia are in terminal groups . The erect branches See also:

• BEAR
• BEAR, BLACK
• BEAR, BROWN
• BEAR, GRIZZLY
• BEAR, ISABELLINE
• BEAR, WHITE

bear three rows of leaves, and spring from a creeping See also:

• AXIS (Lat. for " axle ")

axis from which root-like branches destitute of rhizoids extend into the substratum . Jungermanniaceae Acrogynae.—The plant consists of leafy shoots, the origin of which can be understood in the light of the foliose forms described above . The great See also:

• MAJORITY (Fr. majorite; Med. Lat. majoritas; Lat. major, greater)

majority of existing liverworts belong to this group, the general plan of construction of which is throughout very similar .

In Britain thirty-nine genera with numerous species are found . With few exceptions the stem grows by means of a pyramidal apical cell cutting off three rows of segments . Each segment gives rise to a leaf, but usually the leaves of the ventral row (amphigastria) are smaller and differently shaped from those of the two lateral rows; in a number of genera they are wanting altogether . Sometimes the leaves retain their transverse insertion on the stem, and the two lobes of which they consist are developed equally . More often they come to be obliquely inserted, the anterior edge of each leaf lying under or over the edge of the leaf in front . The two lobes are often unequally developed . In Scapania the upper See also:

• LOBE

lobe is the smaller, while in Radula, Porella and the Lejeuneae this is the case with the lower lobe . The folding of one lobe against another assists in the retention of water . Pitcher-like structures have arisen in different ways in a number of genera, and are especially common in epiphytic forms (Frullania, Lepidolaena, Pleurozia) . In some forms the leaves are finely divided, and along with the See also:

• HAIR (a word common to Teutonic languages)

hair-like paraphyllia form a loose weft around the stem (Trichocolea) . The rhizoids spring from the lower surface of the stem, and sometimes from the bases of the leaves . The branches arise below and by the side of the leaves .

The sexual organs may occur on the same or on distinct individuals: The antheridia are protected by leaves which are often modified in shape . The archegonia are borne at the apex of the main stem or of a lateral branch . A single archegonium may arise from the apical cell (Lejeunea); more commonly a number of others are formed from the surrounding segments . The leaves below the archegonial group are frequently modified in size and shape, but the chief See also:

• PRO

pro-tection is afforded by a tubular perianth, which corresponds to a coherent whorl of leaves and grows up independently of fertilization . The perianth serves also to enclose and protect the sporogonium during its development . In a number of forms belonging to different groups the end of the stem on which the sporogonium is borne grows A downwards so as to form a hollow tubular See also:

• SAC

sac enclosing the sporogonium; in other cases this marsupial sac is formed by the base of the sporogonium .See also:

• BORING

boring into the thickened end of the stem . The sac usually penetrates into the soil and bears rhizoids on its outer surface . Kantia, Calypogeia and Saccogyna are British forms, which have their sporogonie. protected in this way . The sporogonium is very similar throughout the group (figs . 8, 9) . At maturity the seta elongates rapidly, and the wall of the capsule splits more or less completely into four valves, allowing the elaters and spores to escape . In the Jubuloideae, which in other respects form a well-marked group, the seta is short and the elaters extend from the upper part of the capsule to the base; at dehiscence they remain fixed to the valves into which the capsule splits .

The germinating spore usually forms a short filament, but in other cases a flat plate of cells growing by a two-sided apical cell is first formed (Radula, Lejeunea) . In one or two tropical forms the pro-embryonic stage is prolonged, and leafy shoots only arise in connexion with the sexual organs . In Protocephalozia, which grows on bare earth in See also:

• SOUTH
• SOUTH, ROBERT (1634–1716)

South See also:

• AMERICA

America, this pro-embryo is filamentous, while in Lejeunea Metzgeriopsis, which grows on the leaves of living plants, it is a flat branched thallus closely applied to the substratum . Other cases of the plant being, with the exception of the sexual branches, apparently thalloid, are on the other hand to be ex- FIG . 9.—Cephalozia bicuspidata. plained as due to the re- Longitudinal section of the summit of a duction of the leaves and shoot bearing a nearly mature sporoflattening of the stem of a gonium, sg, still enclosed in the cal-shoot (Pteropsiella, Zoopsis). yptra ; at", archegonia which have re- The Acrogynous Junger- mained unfertilized; st, stem; b, leaf. manniaceae fall into a p, perianth . (After See also:

• HOFMEISTER, WILHELM FRIEDRICH BENEDICT (1824-1877)

Hofmeister.) number of natural groups, which cannot, however, be followed out here . They occur in very various situations, on the ground, on rocks and stones, on tree trunks, and, in the damp tropics, on leaves . Usually they form larger or smaller tufts of a green See also:

• COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour, but some forms have a reddish tint . Anthocerotales.—This small and very natural group includes the three genera Anthoceros, Dendroceros and Notothylas, and stands in From Strasburger's Text-book of Bo- tany . many respects in an isolated position among the Bryophyta . Three species of Anthoceros occur in Britain, growing on the damp soil of fields, ditches, &c . The dark green thallus has an ill-defined midrib, and is composed of parenchymatous cells .

In each assimilating cell there is usually a single large chloroplast . The apical region, which has a single initial cell, is protected by mucilage secreted by the mucilage slits, which are small See also:

• PIT (O. E. pytt, cognate with Du. put, Ger. Pfutze, &c., all ultimately adaptations of Lat. puteus, well, formed from root pu-, to cleanse, whence gurus, clean, pure)

pit-like depressions between superficial cells of the lower surface . Mucilage is also often formed in inter-cellular spaces within the thallus . Colonies of Nostoc are constantly found living in some of the mucilage slits which then become enlarged . The sexual organs are scattered over the upper surface . The stalked globular antheridia are exceptional in being formed endogenously, and are situated in groups in special intercellular spaces . The superficial layer of cells bounding the cavity does not break down until the antheridia are nearly mature . Occasion-ally antheridia develop on the surface of shaded portions of the thallus . The necks of the archegonia hardly project above the general surface of the thallus . In structure and development they agree with other Hepaticae, though differences of detail exist . The young sporogonium is protected by a thick calyptra derived from the tissue of the thallus around the archegonium . The sporogonium consists of a large bulbous foot, the superficial cells of which grow out into processes, and a long capsule, which continues to grow for months by the activity of a See also:

• ZONE (Gr. 'WV77, a girdle, from 'wvvLvay to gird)

zone of cells between it and the foot, and may attain the length of an See also:

• INCH (O. Eng. ynce from Lat. uncia, a twelfthpart; cf. " ounce," and see As)

inch and a half .

The wall of the capsule is several layers of cells thick, and since the epidermis contains functional stomata and the underlying cells possess chlorophyll it is capable of assimilation . In the centre of the capsule is a strand of narrow elongated cells forming the columella, and between this and the wail spores mixed with elaters are formed from the See also:

• DOME (Lat domus, house; Ital. duomo, cathedral)

dome-shaped archesporium, the origin of which has already been described (fig . 4, D) . The capsule opens by splitting into two valves from the apex downwards, and the mature spores escape while others are developing in succession below . In Dendroceros, which grows as an epiphyte in the tropics, the thallus has a well-defined midrib and broad wings composed of a single layer of cells . The capsule is similar to that of Anthoceros, but has no stomata, and the elaters have spirally thickened walls . Some species of Anthoceros agree with it in these respects . Nolothylas resembles Anthoceros in its thallus, but the sporogonium is much smaller . In some species, although the columella and archesporium arise in the usual way, both give rise to mingled spores and elaters, and no sterile columella is developed . Musci (Mosses) . Though the number of species of mosses is far greater than of liverworts, the. group offers much less diversity of form . The sexual generation is always a leafy plant, which is not developed directly from the spore but is borne on a well-marked and usually filamentous protonema .

The general course of the life-history and the main features of form and structure will be best under-stood by a brief account of a particular example . Funaria hygrometrica is a moss of very common occurrence even in towns on the soil of paths, at the foot of walls and in similar places . The small plants grow closely crowded in tufts, and consist of short leafy shoots attached to the soil by numerous See also:

• FINE

fine rhizoids . The latter, in contrast to the rhizoids of liverworts, are composed of rows of elongated cells and are branched . The leaves are simple, and except for the midrib are only one layer of cells thick . The structure of the stem though simple is more complicated than in any liverwort . The superficial cells are thick-walled, and there is a central strand of narrow cells forming a water-conducting tissue . The small strand of elongated cells in the midrib of the leaf runs down into the stem, but is not usually connected with the central strand . The sexual organs are developed in groups at the apices, the antheridial group usually terminating the main axis while the archegonia are borne on a lateral branch . The brown tint of the hair-like paraphyses mixed with antheridia (fig . 15) makes the male branch conspicuous, while the archegonia have to be carefully looked for enclosed by the surrounding leaves (fig . 16, B) .

The sporogonium developed from the fertilized ovum grows by means of a two-sided apical cell (fig . 16 A), and is at first of See also:

• UNIFORM

uniform thickness . After a time the upper region increases in See also:

• DIAMETER (from the Cr. &a, through, µErpov, measure)

diameter and forms IV..3the capsule, while the lower portion forms the long seta and the foot which is embedded in the end of the stem . With the growth of the sporogonium the archegonial wall, which for a time kept See also:

• PACE (through O. Fr. pas, from Lat. passus, step, properly the stretch of the leg in walking, from pandere, to stretch)
• PACE, RICHARD (c. 1482-1536)

pace with it, is broken through, the larger upper part terminated by the neck being carried up on the capsule as the calyptra; while the basal portion remains as a tubular sheath See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round the lower end of the seta (cf. figs . 16, C, and fig . 11, A, B) . The seta widens out at the base of the capsule into a region known as the See also:

• APOPHYSIS (Gr. amrocvves, offshoot)

apophysis . The peripheral cells of the seta are thick-walled, and it has a central strand of elongated conducting cells . In the epidermis of the apophysis functional stomata, similar to those of the higher plants, are present and, since cells containing chlorophyll are present below the superficial layers of the apophysis and capsule, the sporogonium is capable of independent assimilation . The construction of the capsule will be best understood from the median longitudinal section (fig . 11, C) . The central region extending between the apophysis and the operculum is composed of sterile tissue and forms the columella (c) .

Immediately around this is the layer of cells from which the spores will be developed (s), and the layers of cells on either side of this form the walls of the spore-sac, which will contain the spores . Between the wall of the capsule, which is composed of several layers of cells, and the spore-sac is a wide intercellular space (h) bridged across by trabeculae consisting of rows of chlorophyll-containing cells . At the junction of the operculum (d) with the rest of the capsule is a circle of cells forming the A, Germinating spores. s, Wall with brown walls from which of spore; v, vacuole; w, the filaments of chlorophyll- rhizoid. containing cells (b) arise; k, B, Part of a developed proto- young moss-plant; w, its first nema. h, Creeping filament rhizoid . annulus (a), by help of which the operculum is detached at maturity as a small lid . Its removal does not, however, leave the mouth of the capsule wide open, for around the margin are two circles of pointed teeth forming the peristome . These are the thickened cell-walls of a definite layer of cells (p), and appear 12 From Strasburger's Text-book of Botany . (From Goebel's Pilanaenmorphologie, by permission of W . Engelmann.) A, Leafy shoot (g) bearing a young sporogonium enclosed in the calyptra (c) . B, Similar plant with an almost mature sporogonium ; s,seta; f, capsule; c, calyptra . C, Median longitudinal section of a capsule, with the seta gradually widening into the apophysis at its base; d, operculum; p, peristome; a, annulus; c, columella; s, archesporium; h, air-space between the spore-sac and the wall of the capsule . as separate teeth owing to the breaking down of the unthickened cell-walls . The numerous spores which have been developed in the spore sac can thus only escape from the pendulous capsule through narrow slits between the teeth, and these are closed in damp air .

The unicellular spores when supplied with moisture germinate (fig . 12) and give rise to the sexual generation . A filamentous protonema is first developed, some of the branches of which are exposed to the light and contain abundant chlorophyll, while others penetrate the substratum as brown or colourless rhizoids . The moss-plants arise from single projecting cells, and numerous plants may spring from the protonema developed from a single spore . The majority of the mosses belong to the same great group as Funaria, the Bryales . The other two subdivisions of the Musci are each represented by a single genus . In the Andreaeales the columella does not extend to the upper end of the capsule, and the latter opens by a number of lateral slits . The Sphagnales also have a dome-shaped spore-sac continued over the columella, and, though their capsule opens by an operculum, they differ widely from other mosses in the development of the sporogonium as well as in the characters of the sexual generation . The three groups are described separately below, but some more general features of the mosses may be considered here . On the whole mosses grow in drier situations than the liver-worts, and the arrangements they present for the conduction of water in the plant are also more See also:

• COMPLETE

complete and suggest in some cases comparisons with the higher plants . In spite of this, however, they are in great part dependent on the absorption of water through the general surface of the shoot, and the power of rapid imbibition possessed by their cell-walls, the crowded position of the small leaves on the stem, and special adaptations for the retention of water on the surface, have the same significance as in the foliose liverworts . The different appearance of exposed mosses in dry See also:

• WEATHER (O. Eng. weder; the word is common to Teutonic languages; cf. Du. weder, Dan. veir, Icel. ve8r, and Ger. Wetter and Gewitter, storm; the root is wa- to blow, from which is derived " wind ")

weather and after a shower illustrates this relation to the water supply .

The protonema is always a well-marked stage in the life-history . Not only does a moss-plant never arise directly from the spore, but in all cases of vegetative reproduction, apart from the separation of branches by decay of older regions of the plant, a protonema is found . Usually the protonema is filamentous and ceases to be evident after the plants have developed . But in some small mosses (e.g . Ephemerum) it plays the chief part in assimilation and lives on from See also:

• YEAR

year to year . In Sphagnum, Andreaea and some genera of the Bryales the protonema or some of its branches have the form of flat plates or masses of cells . The formation of the moss-plant on the protonema is always from a single cell and is similar in all mosses . The first three walls in this cell intersect one another, and define the three-sided pyramidal apical cell by means of which the shoot continues to grow . In Fissidens and a few other mosses the apical cell is two-sided . The leaves formed by the successive segments gradually attain their normal size and structure . Each segment of the initial cell gives rise to a leaf and a portion of the stem; the branches arise from the lower portion of a segment and stand immediately below a leaf . The leaves may form three See also:

• VERTICAL (from Lat. vertex, highest point)

vertical rows, but usually their arrangement, owing to the direction of the segment walls at the apex, becomes more complicated .

Their growth proceeds by means of a two-sided apical cell, and the midrib does not become more than one cell thick until later . In addition to the leaves the stem often bears hair-like structures of different kinds, some of which correspond to modified branches of protonema . The branched filamentous rhizoids which spring from the lower region of the stem also correspond to protonemal branches . The structure of both stem and leaf reaches a high grade of organization in some mosses . Not only are thick-walled sclerenchymatous cells developed to give rigidity to the periphery of the stem and the midrib of the leaf, but in many cases a special water-conducting tissue, consisting of elongated cells, the end walls of which are thin and oblique, forms a definite central strand in the stem . In the forms in which it is most highly developed (Polytrichaceae) this tissue, which is comparable with the xylem of higher plants, is surrounded by a zone oftissue physiologically comparable to phloem, and in the rhizome may be limited by an endodermis . The conducting strands in. the leaves show the same tissues as in the central strand of the stem, and in the Polytrichaceae and some other mosses are in continuity with it . The independent origin of this conducting See also:

• SYSTEM

system is of great interest for comparison with the vascular system of the sporophyte of the higher plants . The sexual organs, with the exception of the antheridia of Sphagnum, are borne at the apices of the main shoot or of branches . Their general similarity to the mature antheridia and archegonia of liverworts and the main difference in their development have been referred to . The antheridia open by means of a cap cell or groups of cells with mucilaginous contents . The details of construction of the sporogonium are referred to below .

In all cases (except Archidium) a columella is present, and all the cells derived from the archesporium produce spores, no elaters being formed . In a few cases the germination of the spore commences within the capsule . The development of the sporogonium proceeds in all cases (except in Sphagnum) by means of an apical cell cutting off two rows of segments . The first periclinal division in the region forming the capsule separates an inner group of cells (the endothecium) form the peripheral layer (amphithecium) . In Sphagnum, as in Anthoceros, the archesporium is derived from the amphithecium; in all other mosses it is the outermost layer of the endothecium . Vegetative propagation is widely spread in the mosses, and, as mentioned above, a protonema is always formed in the development of the new plant . The social growth of the plants characteristic of many mosses is a result of the formation of numerous plants on the See also:

• ORIGINAL

original protonema and on developments from the rhizoids . Besides this, gemmae may be formed on the protonema, on the leaves or at the apex, and some mosses have specialized shoots for their better protection or distribution . Thus in See also:

• GEORGIA

Georgia the stalked, multicellular gemmae are borne at the ends of shoots surrounded by a rosette of larger leaves, and in Aulacomnium androgynum they are raised on an elongated leafless region of the shoot . In other cases detached leaves or shoots may give rise to new plants, and when a moss is artificially divided almost any fragment may serve for reproduction . Even in those rare cases in which the sexual generation can be developed without the intervention of spore production from the tissues of the sporogonium, a protonema is formed from cut pieces of the seta or in some cases from intact sporogonia still attached to the plant . This phenomenon of apospory was first discovered in mosses, but is now also known in a number of ferns (see PTEamoPHYTA) .

Sphagnales.—The single genus Sphagnum occupies a very distinct and isolated position among mosses . The numerous species, which are familiar as the bog-mosses, are so similar that minute structural characters have to be relied on in their See also:

• IDENTIFICATION (Lat. idem, the same)

identification . The plants occur in large patches of a See also:

• PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; " pole " is from the same original source)

pale green or reddish colour on See also:

• MOORS (Lat. Mauri; Gr. Mavpot, dark men)
• MOORS, KABYLES, MZABITES

moors, and, when filling up small lakes or pools, may attain a length of some feet . Their growth has played a large part in the formation of See also:

• PEAT (possibly connected with Med. Lat. petia, pecia, piece, ultimately of Celtic origin; cf. O. Celt. pet, O. Ir. pit, Welsh peth, portion)

peat . The species are distributed in temperate and arctic climates, but in the tropics only occur at high levels . The protonema forms a flat, lobed, thalloid structure attached to the soil by rhizoids, and the plants ari