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SAXIFRAGACEAE

Online Encyclopedia
Originally appearing in Volume V24, Page 264 of the 1911 Encyclopedia Britannica.
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SAXIFRAGACEAE, in. botany, a small natural order of Dicotyledons belonging to the sub-class Polypetalae and containing 27 genera with about 350 species distributed through the Arctic and north temperate zone, often alpine. It is repre- sented in Britain by its largest genus Saxifrage (q.v.), Chrysosplenium (golden saxifrage) and Parnassia (grass of Parnassus). The plants are herbs, generally with scattered exstipulate leaves with a broad leaf-base. , The small flowers are generally arranged in cymose inflorescences and are bisexual, regular and hypogynous, y' perigynous or more frequently more (~' or less epigynous, this variation in ():.: ~; the relative position of the ovary occurring in one and the same genus Saxifraga (fig. 1). The flowers are FIG. 2.—Diagram of a 5-merous, more rarely 4-merous, saxifrage (Saxifraga tridachaving 5 (or 4) sepals, 5 (or 4) free tylites). The calyx and petals, two 5- or 4-merous whorls of corolla each consist of five free stamens which are obdiploste parts, tl ere are ten stamens i.e. those of the outer whorl of two two carpels. e and a pistil monous, of are opposite to the petals, and two carpels (see fig. 2). The carpels are sometimes free, more generally united at the base, or sometimes completely joined to form a one- or two-chambered ovary with two free styles. The fruit is a many-seeded capsule. More than half the species (20o) are contained in the genus Saxifrage (q.v.). Chrysosplenium, with 39 species, two of which are British, three valves, by means of which 2 3 a s 6 7 8 the compass is rendered chromatic, and which act as in other valve instruments, lowering the pitch of the instrument when depressed, respectively r tone, a semitone and 12 tones; and further, when used in combination, 2 tones, 21 tones and 3 tones . The Flugelhorns, the euphonium, the bornbardon and the tubas are sometimes erroneously classed as saxhorns. The difference between saxhorns and bombardons or tubas consists in the calibre of the bore, which in the latter is sufficiently wide in proportion to the length to produce the fundamental note of the harmonic series an octave below the lowest note of the saxhorns. The consequence of this structural difference is important, for whereas the tube of the tubas is theoretically of the same length as an open organ pipe of the same pitch, the saxhorns require a tube twice that length to produce the same scale. For instance, a euphonium sounding 8 ft. C only needs a tube 8 ft. long, whereas the corresponding bass saxhorn requires one 16 ft. long. In Germany these structural differences have given rise to a classification of brass wind instruments as whole or half instruments (Ganze or Halbe),' according to whether the whole or only the half of the length of tubing is of practical use. The members of the saxhorn family are the small saxhorn in Eb, the soprano in Bb, the alto in Eb, the tenor in Bb, the bass in Bb (an octave lower), the low bass in Eb, the contra-bass in Bb, three octaves below the soprano. All the saxhorns are treated as transposing instruments .2 A similar family, constructed with rotary valves and conical tubes of larger calibre than the saxhorns, but having the same harmonic scale, is known in Germany as Flugelhorn. (K. S.) has a very similar distribution. The North American genus Heuchera has sometimes apetalous flowers. Astilbe has 6 species in temperate Asia and north-eastern North America; A. japonica is commonly grown in the spring as a pot-plant, and often misnamed Spiraea. The order is frequently much extended to include other groups of genera differing in habit and more or less in general conformation from those to which the order is here confined, and which are then regarded as forming one of several tribes. Among these is the order Ribesiaceae, comprising one single genus Ribes, to which belong the gooseberry (R. Grossularia) and currants of gardens. These are shrubs with racemes of flowers which have only one whorl of stamens (isostemonous), an inferior unilocular ovary with two parietal placentas, and fruit a berry. Another is the Hydrangeaceae, to which belong Hydrangea (q.v.), Deutzia and Philadelphus, all well-known garden plants; P. coronarius is the so-called Syringa or mock-orange. They are shrubs or trees with simple generally opposite leaves, 5-merous flowers with epigynous stamens and a 3- to 5-locular ovary. Escallonia, which represents a small group of genera with leathery gland-dotted leaves, is also often included.
End of Article: SAXIFRAGACEAE
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