The chief value of the potato as an article of diet consists in the starch it contains, and to a less extent in the potash and other salts. The quantity of nitrogen in its composition is small, and hence it should not be relied on to constitute the staple article of diet, unless in admixture with milk or some other substance containing nitrogen. Letheby gives the following as the average composition of the potato— [table]

—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 (Dehérain, Cours de Chimie Agricole, p. 159). Boussingault gives 25 - 2 per cent, of starch and 3 per cent, of nitrogenous matter. Warington states that the proportion of nitrogenous to non-nitrogenous matter in the digestible part of potatoes is as 1 to 10 - 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 per cent, of potash, and 19 ’ 1 per cent, 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.

The origin and history of the potato are better known than in the case of many long-cultivated plants. It is to the Spaniards that we owe this valuable esculent, “optimum benigni Numinis donum, dapes grata diviti, pauperi panis,” as it has been called by an eminent botanist. The Spaniards met with it in the neighbourhood of Quito, where it was cultivated by the natives. In the Cronica de Peru of Pedro Cieça, published at Seville in 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 de l ’ Escluse, sa Vie et ses Oeuvres, and to which we are indebted for some of the historical details given below, states that the potato was introduced from Santa Fé 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 our potato but the Sweet Potato (see below).

In 1587 or 1588 De l ’ Escluse, better known under the Latinized appellation of “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 Chili to New Granada, but not in Mexico. Nearly a hundred years afterwards, in 1585 or 1586, potato tubers were brought from North Carolina and Virginia 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 introduced under the auspices of Raleigh were thus imported a few years 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. Be this as it may, 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.” Gerard says—

“The roote is thicke, fat and tuberous; not much differing either in shape, colour or taste from the common Potatoes, saving that the rootes hereof are not so great nor long; some of them as round as a ball, some ouall or egge-fashion, some longer and others shorter; which knobbie rootes are fastened unto the stalks with an infinite number of threddie strings. . . . It groweth naturally in America where it was first discovered, as reporteth C. Clusius, since which time I have received rootes hereof from Virginia otherwise called Norembega which growe and prosper in my garden, as in their owne native countrie.”

The “common Potatoes” of which Gerard speaks are the tubers of Convolvulus batatas, the Sweet Potato, which nowadays would not in Great Britain be spoken of as common. Evidently the author attached great importance to the potato, for in the frontispiece to his volume he is represented with the flower and foliage of the plant in his hand. In his opinion it was, like the common potato, “a foode as also a meate for pleasure equall in goodnesse and wholesomenesse unto the same, being either rosted in the embers, or boiled and eaten with oile, vinegar and pepper, or dressed any other way by the hand of some cunning in cookerie.” A second edition of the Herbal was published in 1636 by Thomas Johnson, with a different illustration from that given in the first edition, and one which in some respects, as in showing the true nature of the tuber, is superior to the first. The phenomenon of growing out or “super-tuberation” is shown in this cut.

Previous to this (in 1629) Parkinson, the friend and associate of Johnson, had published his Paradisus, in which (p. 517) he gives an indifferent figure of the potato under the name of Papas seu Battatas Virginianorum, and adds details as to the method of cooking the tubers which seem to indicate that they were still luxuries rather than necessaries. 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 insui ae” 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, who derived the plant from Peru or other parts of South America, and perhaps provisioned their ships with its tubers. In any case 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.

The source of the potato being known, it is a matter of interest to determine the particular species from which the cultivated forms have descended and the exact part of the great American continent in which it is indigenous. As to the first point, 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 native in Chili, but it is very doubtful if it is truly wild farther north. Mr Baker (Journal of the Linnean Society, vol. xx., 1884, p. 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 synonymous or trifling variations. The six admitted tuber-bearing species are S. tuberosum, S. Maglia, S. Commersoni, S. cardioplιyllum, S. Jamesii, and >S'. oxy carpum. S. tuberosum is, according to Mr Baker, a native not only of the Andes of Chili 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 the American continent have no claim to be considered absolutely wild, but are the descendants of cultivated forms. S. Alaglia is a native of the Chilian coast as far south as the Chonos Archipelago, and was cultivated in the garden of the Horticultural Society at Chiswick in 1822, being considered by Sabine, in his paper on the native country of the wild potato, to be the true o. tuberosum and the origin of the cultivated forms. This species was also found by Darwin in Chili, and was considered by him, as by Sabine before him, to be the wild potato. It is remarkable, says Darwin, that the same plant should be found in the sterile mountains of.central Chili, where a drop of rain does not fall for moιe than six months, and within the damp forests of these southern (Chonos) islands. The explanation, according to Baker, is that the plant of the dry mountains is S. tuberosum, that of the coast is S. Maglia. It must, however, be stated that, although Mr Baker refers to the plants figured by Sabine (Trans. Hort. Soc. Land., vol. v. p. 249) as being without doubt S. Alaglia, A. de Candolle (Origine des Plantes cultivées, p. 40) is equally emphatic in the opinion, “ce qui saute aux yeux,” that the plant grown from Chilian tubers and figured in the plate before cited is S. tuberosum. S. Commersoni occurs in Uruguay, Buenos Ayres, and the Argentine Republic, in rocky situations at a low level. Under the name of S. Ohrondii it has lately been introduced into western France, where it is not only hardy but produces abundance of tubers, which are palatable, but have a slightly acid taste. The tubers give promise of improvement under cultivation. S. cardiophyllum, described by Lindley in the Journal of the Horticultural Society, is a native of the mountains of central Mexico at elevations of 8000 to 9000 feet. 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, but as the plant is now in cultivation in England it may be expected to improve in this particular. S. oxycarpum is stated by Mr Baker to be a little known but very distinct tuberous species from central Mexico.

Mr Baker looks upon the forms enumerated not only with the eye of a systematic botanist but with the tendencies of one whose object is to assign varying forms to one common type from which they have, or may probably have, arisen. But from a practical point of view the forms in question require careful analysis rather than synthesis. Their morphological peculiarities and chemical constitution deserve attentive consideration as to then-degree of constancy, and more particularly as to any relation that may be traced between them and the climatic circumstances under which they grow naturally, and their power of resistance to the attacks of disease. 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, which would injure the early sorts, it is, on the other hand, undesirable, because late varieties are more liable to be attacked by the potato disease, which as a rule makes its appearance at or about the time when the earliest varieties are ready for lifting, but before the late varieties are matured, and consequently while they are still exposed to the destructive influences of the fungus.

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, <fcc. It is probable that a more careful investigation of these peculiarities, and especially of those connected with the microscopical anatomy of the leaves, would give serviceable indications of the varieties most or least susceptible to the disease,— a point at present hardly if at all attended to. As to the tubers, they vary greatly in size, form, and colour; gardeners divide them into rounded forms and long forms or “kidneys”; “lapstones” are more or less flattened; and “pebble” varieties are long potatoes broader at one end than at the other. 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 originated chiefly by cross-breeding, but not invariably so, as some varieties rarely, if ever, produce flowers in Britain, and yet “sports” have been observed in their tubers and have become the parents of new varieties. Various methods have been proposed for the prevention or arrest of the ravages of the fungus which causes the “potato disease” (see below). In addition to different modes of cultivation, attempts have been made to secure varieties less liable than others to disease, and, although no great measure of success has been attained, still the matter is not without promise, seeing how the early varieties, as before stated, escape the full virulence of the malady. Other attempts have been made to infuse a hardier constitution by hybridizing the potato with hardy species such as N. Dulcamara and S. nigrum. Hybrids were accordingly raised by Mr Maule, but they all suffered from the disease as much as the parents, and it is to be feared that the hybrids raised between the common potatoes and some of the six species mentioned by Mr Baker may suffer a like fate. This, however, remains to be proved. Mr Maule, disappointed with his hybridization experiments, then tried the effect of grafting. With this view he grafted S. nigrum on to a shoot of the potato. New tubers were formed, the foliage being wholly that of N. nigrum. In another experiment he grafted the potato on to S. Dulcamara. In one case tubers were produced on the graft (the potato), but none on the Dulcamara stock, either above or below ground, while in another case tubers were actually produced on the underground portions of S. Dulcamara. Mr Maule’s experiments were most ingenious, but the theory he gave in his The Potato, what is it? (Bristol, 1876) will not commend itself to physiologists, and there is no evidence to show whether the grafts he obtained were attacked by the parasite or even whether they had a chance of being so. Mr Maule’s experiments, especially the one last mentioned, afford confirmation of the possibility of graft hybridization being effected. Various experimenters, especially Mr Fenn, have asserted that by engrafting an eye of one variety into the tuber of another, not only will adhesion take place but the new tubers will present great variety of character; and this indeed seems to be the case from the numerous specimens shown by Mr Fenn at the Royal Horticultural Society, but it can hardly be considered as established that the variations in question were the result of any commingling of the essences of the two varieties. The wound may simply have set up that variation in the buds the occasional existence of which has been already noted. The last-cited experiment of Mr Maule’s, however, is much more conclusive. Mr A. Dean also {Gardeners' Chronicle, 2d September 1876, p. 304)

succeeded in grafting the potato on to the tomato, with the result that, although no tubers were found on the root of the tomato, numerous tubers were produced on the sides of the branches of the potato. Another experiment may be here mentioned as throwing light on the formation of tubers, one wherein Mr Burbidge observed the production of tubers at the portion of an ordinary cutting of S. Commersoni inserted in the soil. In this case no tubers were formed above ground. (μ. τ. μ ) Potato Disease.

There are few agricultural subjects of greater importance than the culture of the potato and the losses entailed by potato disease. The number of acres in Great Britain alone under cultivation for potatoes is generally more than half a million (543,455 in 1883, 562,344 in 1884); the average weight of the produce...