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POTATO (Solanum tuberosum)

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Originally appearing in Volume V22, Page 202 of the 1911 Encyclopedia Britannica.
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POTATO (Solanum tuberosum), a well-known plant which owes its value to the peculiar habit of developing underground slender leafless shoots or branches which differ in character and office from the true roots, and gradually swelling at the free end produce the tubers (potatoes) which are the common vegetable food. The nature of these tubers is further rendered evident by the presence of " eyes " or leaf-buds, which in due time lengthen into shoots and form the haulm or stems of the plant. Such buds are not, under ordinary circumstances, formed on roots. The determining cause of the formation of the tubers is not certainly known, but Professor Bernard has suggested that it is the presence of a fungus, Fusarium solani, which, growing in the underground shoots, irritates them and causes the swelling; the result is that an efficient method of propagation is secured independently of the seed. Starch and other matters are stored up in the tubers, as in a seed, and are rendered avail-able for the nutrition of the young shoots. When grown under natural circumstances the tubers are relatively small and close to the surface of the soil, or even lie upon it. In the latter case they become green and have an acrid taste, which renders them unpalatable to human beings, and as poisonous qualities are produced similar to those of many Solanaceae they are unwholesome. Hence the recommendation to keep the tubers in cellars or pits, not exposed to the light. Among the nine hundred species of Solanum less than a dozen have this property of forming tubers, but similar growths are formed at the ends of the shoots of the common bramble, of Convolvulus sepium, of Helianthus tuberosus, the so-called Jerusalem artichoke, of Sagittaria, and other plants. Tubers are also sometimes formed on aerial branches, as in some Aroids, Begonias, &c. The production of small green tubers on the haulm, in the axils -bf the leaves of the potato, is not very unfrequent, and affords an interesting proof of the true morphological nature of the unclgr ground shoots and tubers. This phenomenon follows injury to the phloem in the lower parts of the stem, preventing the downward flow of elaborated sap. The injury may be due to gnawing insects, and particularly to the fungus Corticium vagum, var. Solani (Rhizoctonia). The so-called fir-cone potatoes, which are elongated and provided with scales at more or less regular intervals, show also very clearly that the tuber is only a thickened branch with " eyes " set in regular order, as in an ordinary shoot. The potato tuber consists mainly of a mass of cells filled with starch and encircled by a thin corky rind. A few vessels and woody fibres traverse the tubers. of the potato- composition The chief value of the potato as an article of diet consists in ~ edition of the Herbal was published in 1636 by Thomas Johnson, the starch it contains, and to a less extent in the potash and other with a different illustration from that given in the first edition, salts. The quantity of nitrogen in its composition is small, ; and one which in some respects, as in showing the true nature and hence it should not be relied on to constitute the staple of the tuber, is superior to the first. The phenomenon of growing article of diet. Letheby gives the following as the average out or " super-tuberation " is shown in this cut. Previous to this (in 1629) Parkinson, the friend and associate matters . 2.1 Saline matter . 0.7 of Johnson, had published his Paradisus, in which (p. 517) he 18.8 Water . . . 75.0 gives an indifferent figure of the potato under the name of Papas 3'2 seu Battatas Virginianorum, and adds details as to the method 0.2 loons Nitrogenous Starch, &c. Sugar Fat -a result which approximates closely to the average of nineteen analyses cited in How Crops Grow from Grouven. In some analyses, however, the starch is put as low as 13.30, and the nitrogenous matter as 0.92 (Deherain, Cours de chimie agricole, p. 1J9). Boussingault gives 25'2% of starch and 3% of nitrogenous matter. Warington states that the proportion of nitrogenous to non-nitrogenous matter in the digestible part of potatoes is as r to io•6. The composition of the tubers evidently varies according to season, soils, manuring, the variety grown, &c., but the figures cited will give a sufficiently accurate idea of it. The " ash " contains on the average of thirty-one analyses as much as 59'8% of potash, and 19.1% of phosphoric acid, the other ingredients being in very minute proportion. Where, as in some parts of northern Germany, the potato is grown for the purpose of manufacturing spirit great attention is necessarily paid to the quantitative analysis of the starchy and saccharine matters, which are found to vary much in particular varieties, irrespective of the conditions under which they are grown. It is to the Spaniards that we owe this valuable esculent. The Spaniards met with it in the neighbourhood of Quito, where it was cultivated by the natives. In the Cronica de Peru of Pedro Ciega (Seville, 1553), as well as in other Spanish books of about the same date, the potato is mentioned under the name '` battata " or " papa." Hieronymus Cardan, a monk, is supposed to have been the first to introduce it from Peru into Spain, from which country it passed into Italy and thence into Belgium. Carl Sprengel, cited by Professor Edward Morren in his biographical sketch entitled Charles do l'Escluse, sa vie et ses oeuvres, states that the potato was introduced from Santa Fe into England by John Hawkins in 1563 (Garten Zeitung, 1805, p. 346). If this be so, it is a question whether the English and not the Spaniards are not entitled to the credit of the first introduction; but, according to Sir Joseph Banks, the plant brought by Drake and Hawkins was not the common English potato but the sweet potato. In 1587 or 1588 De 1'Escluse (Clusius) received the plant from Philippe de Sivry, lord of Waldheim and governor of Mons, who in his turn received it from some member of the suite of the papal legate. At the discovery of America, we are told by Humboldt; the plant was cultivated in all the temperate parts of the continent from Chile to Colombia, but not in Mexico. In 1585 or 1586, potato tubers were brought from what is now North Carolina to Ireland on the return of the colonists sent out by Sir Walter Raleigh, and were first cultivated on Sir Walter's estate near Cork. The tubers introduce under the auspices of Raleigh were thus imported a few y_e'ass `later than those mentioned by Clusius in 1588, which must have been in cultivation in Italy and Spain for some years prior to that time. The earliest representation of the plant is to be found in Gerard's Herbal, published in 1597. The plant is mentioned under the name Papus orbiculatus in the first edition of the Catalogus of the same author, published in 1596, and again in the second edition, which was dedicated to Sir Walter Raleigh (1599). It is, however, in the Herbal that we find the first description of the potato, accompanied by a woodcut sufficiently correct to leave no doubt whatever as to the identity of the plant. In this work (p. 781) it is called " Battata virginiana sive Virginianorum, et Pappus, Potatoes of Virginia." The " common potatoes " of which Gerard speaks are the tubers of I pomoea Batatas, the sweet potato, which nowadays would not in Great Britain be spoken of as common. A secondof cooking the tubers which seem to indicate that they were still luxuries. Chabraeus, who wrote in 1666, tells us that the Peruvians made bread from the tubers, which they called " chunno." He further tells us that by the natives Virginieae insulae the plant was called " openauk," and that it is now known in European gardens, but he makes no mention of its use as an esculent vegetable, and, indeed, includes it among " plantae malignae et venenatae." Heriot (De Bry's Collection of Voyages), in his report on Virginia, describes a plant under the same name " with roots as large as a walnut and others much larger; they grow in damp soil, many hanging together as if fixed on ropes; they are good food either boiled or roasted." The plant (which is not a native of Virginia) was probably introduced there in consequence of the intercourse of the early settlers with the Spaniards. The cultivation of the potato in England made but little progress, even though it was strongly urged by the Royal Society in 1663; and not much more than a century has elapsed since its cultivation on a large scale became general. Botanists are agreed that the only species in general cultivation in Great Britain is the one which Bauhin, in his Phytopinax, p. 89 (1596), called Solanum tuberosum esculentum, a name adopted by Linnaeus (omitting the last epithet), and employed by all botanical writers. This species is probably native in Chile, but it is very doubtful if it is truly wild farther north. Baker (Journ. Linn. Soc., 1884, xx. 489), has reviewed the tuber-bearing species of Solanum from a systematic point of view as well as from that of geographical distribution. Out of twenty so-called species he considers six to be really distinct, while the others are merely synonyrnous or trifling variations. The six admitted tuber-bearing species are S. tuberosum, S. Maglia, S. Commersoni, S. cardiophyllum, S. Jamesii and S. oxycarpum. S. tuberosum is, according to Mr Baker, a native not only of the Andes of Chile but also of those of Peru, Bolivia, Ecuador and Colombia, also of the mountains of Costa Rica, Mexico and the south-western United States. It seems most probable, however, that some at least of the plants mentioned in the northern part of America are the descendants of cultivated forms. S. Maglia is a native of the Chilean coast as far south as the Chonos Archipelago, and was cultivated in the garden of the Horticultural Society at Chiswick in 1822, being con- sidered by Sabine, in his paper on the native country of the wild potato, to be the true S. tuberosum and the origin of the cultivated forms. This species was also found by Darwin in Chile, and was considered by him, as by Sabine before him, to be the wild potato. Baker refers to the plants figured by Sabine (Trans. Hort. Soc. Lond. v. 24.9) (fig. 1) as being without doubt S. Maglia, but A. de Candolle (Origine des Plan.tes cultivees, p. 40) is equally emphatic in the opinion that it is S. tuberosum. S. Commersoni occurs in Uruguay, Buenos Aires and the Argentine Republic, in rocky situations at a low level. Under (From Sabine's figure in the Trans. Hart. the name of S. Ohrondii it has Soc. Lond., 1324, vol. v. pl. ii. See been introduced into western text.) France, where it is not only FIG. i.—Wild Potato-plant in hardy but produces abundance bloom. (- nat. size.) of tubers, which are palatable, but have a slightly acid taste. S. cardiophyllum, described by Lindley in the Journ. Hort. Soc. is a native of the mountains of central Mexico at elevations of 8000 to 9000 ft. S. Jamesii is a well-defined species occurring in the mountains of Colorado, New Mexico and Arizona, and also in Mexico. In a wild state the tubers are not larger than marbles. S. oxycarpum is a but very distinct tuberous species from POTATO central I The full-sized tubers are, however, preferable to smaller ones, as their larger buds tend to produce stronger shoots, and where cut sets are used the best returns are obtained from sets taken from the points of the tubers—not from their base. Thomas Dickson of Edinburgh long ago observed that the most healthy and productive crop was to be obtained by planting unripe tubers, and proposed this as a preventive of the disease called the " curl," which sometimes attacks the young stems, causing them and also the leaves to become crumpled, and few or no tubers to be produced; in this connexion it is interesting to note that Scottish and Irish seed potatoes give a larger yield than English, probably on account of their being less matured. It has also been noted that the sprouting of the eyes of the potato may be accelerated if, while still unripe, it is taken up and exposed for some weeks to the influence of a scorching sun. The best sets are those obtained from plants grown in elevated and open situations, and it is also beneficial to use sets grown on a different soil. The earliest crops should, if possible, be planted in a light soil and in a warm situation, towards the end of February, or as early as possible in March. In some cases the tubers for early crops are sprouted on a hotbed, the plants being put out as soon as the leaves can bear exposure. The main crop should be planted by the middle of March, sprouted sets being used; late planting is very undesirable. Those in-tended for storing should be dug up as soon as they are fairly ripe, unless they are attacked by the disease, in which case they must be taken up as soon as the murrain is observed; or if they are then sufficiently developed to be worth preserving, but not fully ripe, the haulms or shaws should be pulled out, to prevent the fungus passing down them into the tubers; this may be done without disturbing the tubers, which can be dug afterwards. Forcing.—The earliest crop may be planted in December, and successional ones in January and February; the varieties specially suited for forcing being chosen. The mode of cultivation adopted by the London market gardeners is thus in substance explained by Cuthill: A long trench, 5 ft. wide and 2 ft. deep, is filled with hot dung, on which soil to the depth of 6 in. is put. The sets employed are middle-sized whole potatoes, which are placed close together over the bed, covered with 2 in. of mould, and then hooped and protected with mats and straw, under which conditions they will sprout in about a month. A bed of the requisite length (sometimes 10o yds.) is then prepared of about 2 ft. thickness of hot dung, soil is put on to the depth of 8 in., and the frames set over all. The potatoes are then carefully taken up from the striking bed, all the shoots being removed except the main one, and they are planted 4 in. deep, radishes being sown thinly over them and covered lightly with mould. When the haulm of the potato has grown to about 6 in. in height the points are nipped off, in order to give the radishes fair play; and, although this may stop growth for a few days, still the potato crop is always excellent. After planting nothing more is required but to keep up the temperature to about 7o°, admitting air when practicable, and giving water as required. The crop is not dug up until it has come to maturity. Potatoes are also grown largely in hooped beds on a warm border in the open ground. The sets after having been sprouted, as above, are planted out in January in trenches 2 ft. deep filled with hot dung, the sets being planted 5 in. deep, and over all radishes are sown. The ridges are then hooped over, allowing about 2 ft. of space in the middle, between the mould and the hoop, and are covered with mats and straw, but as soon as the radishes come up they are uncovered daily, and covered again every night as a protection against possible frosts. This is continued till the potatoes are ready for digging in May. Potatoes are sometimes grown in pots in heat, sprouted sets being planted in 11-in. pots about two-thirds full of soil, and placed near the glass in any of the forcing-houses, where a temperature of from 65° to 7o° is to be maintained. The plants are duly watered and earthed up as they advance in growth. little known Mexico.' A review of the localities in which the presence of S. tuberosum and its tuber-bearing allies has been ascertained shows that, broadly, these varieties may be divided into mountainous and littoral. In either case they would not be subjected, at least in their growing season, to the same extremes of heat, cold and drought as plants growing on inland plains. Again, those forms growing at a high elevation would probably start into growth later in the season than those near the coast. The significance of these facts from a cultural point of view is twofold: for, while a late variety is desirable for culture in Great Britain, as ensuring more or less immunity from spring frost, it is, on the other hand, undesirable, because late varieties are more liable to be attacked by the potato disease (Phytophthora infestans) which as a rule appears about the time when the earliest varieties are ready for lifting, but before the late varieties are matured. In cultivation the potato varies very greatly not only as to the season of its growth but also as to productiveness, the vigour and luxuriance of its foliage, the presence or relative absence of hairs, the form of the leaves, the size and colour of the flowers, &c. The tubers vary greatly in size, form and colour; gardeners divide them into rounded forms and long forms or " kidneys," and there are of course varieties inter-mediate in form. The colour of the rind, yellowish, brown or purple, furnishes distinctions, as does the yellow or white colour of the flesh. The colour of the eyes and their prominence or depression are relatively very constant characteristics. These variations have arisen chiefly through cross-breeding, though not entirely so, there being a few cases upon record of the production of " sports " from tubers that have become the parents of new varieties, but authentic cases of the sporting of tubers are few and far between. If, on the other hand, the true seeds of any of our cultivated varieties are sown, the seedlings show very wide variations from one another and from the parents. In this connexion it is very interesting to observe that Messrs Sutton of Reading find that the seedlings of many of the varieties of potato that occur spontaneously in different parts of America come quite true to type from seed. The potato thrives best in a rather light friable loam; and in thin sandy soils the produce, if not heavy, is generally of very good quality. Soils which are naturally wet and heavy, as well as those which are heavily manured, are not suitable. Indeed it is best, except when there is ample space, to grow only the earlier kinds in gardens. If the soil is of fair quality the less manure used upon it the better, unless it be soot or lime. Gypsum, bone-dust, superphosphate of lime and nitrate of soda may also be used, and wood ashes are advantageous if the soil contains much vegetable matter; but the best results are usually obtained when farmyard manure is supplemented by artificials, not by using artificials alone. Potatoes arc commonly propagated by planting whole tubers or by dividing the tubers, leaving to each segment or " set " one or two eyes or buds. The " sets " are then planted in rows at a distance varying from 15 in. to 3 ft., the distance being regulated by the height of the stems, and that between the sets varying from 6 to 12 in., 8 in. being a good average space for garden crops, with 2 ft. between the rows. The sets may be put in 6 in. deep. The planting of whole tubers instead of the cut sets usually gives a better return. ' Although these six are the only species admitted as such by Baker, it is well to note some of the varieties. The S. etuberosum of Lindley, differing from the common S. tuberosum in not producing tubers, was found in Chile, and is probably not specifically distinct, although exceptional, for it is by no means very unusual to find even cultivated plants produce no tubers. S. Fernandezianum is, according to Baker, a form of S. tuberosum, but if so its habitat in the mountain woods of Juan Fernandez is climatically different from that in the dry mountains of central Chile, where the true S. tuberosum grows. S. otites was found more recently by Andre on the summit of Quindiu in Colombia, at a height of 11,483 ft. It produces tubers of the size of a nut. S. Andreanum, found by Andre at Cauca (6234 ft.), was considered by the traveller to be the true S. tuberosum, but this view is not shared by Baker, who named it after the discoverer. Its tubers, if it produces any, have not been seen. S. immite is probably only a slight variety of S. tuberosum, as are also the Venezuelan S. colombianum, S. verrucosum, S. demissum and S. utile. S. Fendleri, a native of the mountains of New Mexico and Arizona, was considered by Asa Gray to be likewise a form of S. tuberosum.
End of Article: POTATO (Solanum tuberosum)

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