1902 Encyclopedia > Potato


POTATO. The potato (Solarium tuberosum) is too well known to need detailed description. It 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 which gradually swell at the free end and thus produce the tubers with which we are so familiar. 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 I haulm or stems of the plant. Such buds are not, under ordinary circumstances, formed on roots. What the determining cause of the formation of the tubers may be is not known j the object evidently is to secure a method of propagation independently of the seed. Starch and other matters are stored up in the tubers, as in the perisperm of a seed, and in due season are rendered avail-able for the nutrition of the young shoots when they begin to grow. The young shoots, in fact, derive their nourishment from the parent tuber until by the produc-tion of roots and leaves they are enabled to shift for themselves. When grown under natural circumstances (without being earthed up, as is usually done by the cultivator) 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 would probably render them objectionable to predatory animals or insects, and which certainly renders them unpalatable to human beings, and, in consideration of the known poisonous qualities of many Solanacex, might probably sause them to be unwholesome. Hence the recommenda-tion to keep the tubers in cellars or pits, not exposed to the light, for the green colouring matter is, in this case, developed in the tubers independently of the direct action of light on the leaves. Among the six 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 the Convolvulus sepium, of the Helianthus tuberosus, the so-called Jerusalem arti-choke, 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 of the leaves of the potato, is not very unfrequent, and affords an interesting proof of the true morphological nature of the underground shoots and tubers. 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.

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Saline matter

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—
Nitrogenous matters 21
Starch, &c 18-8
Sugar 3-2
Fat 0-2
—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. 159). Boussingault gives 25-2 per cent, of starch and 3 per cent, of nitrogenous matter. Warington states that the proportion of nitro-genous 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, manur-ing, 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"! 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 con-ditions 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, how-ever, 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 sen 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. Chabrseus, 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 " Virginieaz insulse" 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, in-deed, includes it among "plantse malignse et venenatae." Heriot (De Bry's Collection of Voyages), in his report ja 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 pro-gress, 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, eseidentum, 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. cardiophyllum, S. Jamesii, and S. oxycarpum.

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, how-ever, 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. Maglia 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 j>aper 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 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 more 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. Sort. Soc. Zand., vol. v. p. 249) as being without doubt S. Maglia, 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. cardio-phyllum, 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 their 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 moun-tainous 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 1 the potato varies very greatly not only as to the season of its growth but also as to productive-ness, 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. It is probable that a more careful investigation of these peculiarities, and especially of those connected with the microscopical ana-tomy 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 S. Dulcamara and .5. 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 S. nigrum. In another experiment he grafted the potato on to S. Dulcamara. In one case tubers were produced on the graft (the potato), out none on the Dulcamara stock, either above or below ground, while in another case tubers were actually pro-duced 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)

1 See HORTICULTURE, vol. xii. p. 286.

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. (M. T. M.)


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 per acre may be taken at five tons, the average price about £65 per ton, so that the commercial value of each year's crop commonly ranges between £613,000,000 and £615,000,000. It is not unusual in bad seasons for a single grower to lose from £61000 to £61500 through disease; for the market grower some-times not only loses the entire produce, or nearly so, but loses also the value of the seed, the guano, the farm-yard manure, the rent, and the labour. Growers sometimes lose £630 per acre in one season, for, exclusive of the dis-eased produce, £610 may be put down to guano and dung, £64, 10s. to rent, tithes, and taxes, £66, 10s. for seed, and £62 for digging; added to this there are ploughing, har-rowing, overlooking, earthing up, sacks, carriage to and fro, and many minor expenses. The losses range in amount according to the virulence and general extent of the dis-ease. In extreme cases every tuber is lost, as the produce will not even pay the cost of lifting. The year of the great potato famine in Britain was 1845, but the Rev. M. J. Berkeley, in his famous essay on the potato murrain published by the Royal Horticultural Society of England in 1846, stated that a very serious disease of the potato named the " curl" had at that time been known in Britain for more than half a century. We now know that the " curl" is a condition of the true potato murrain. As a rule, although there are a few exceptions, the disease occurs wherever the potato is grown. It is known in South America, in the home of the potato plant.

The disease of potatoes is caused by the growth of a fungus named Peronospora infestans, Mont., within the tissues of the host plant, and this fungus has the peculiar property of piercing and breaking up the cellular tissues, and setting up putrescence in the course of its growth. The parasite, which has a somewhat restricted range of host plants, chiefly invades the potato, Solanum tuberosum, L.; the bittersweet, S. Dulcamara, L.; S. demissum, Lind.; and S. cardiophyllum, Lind. It is also very destructive to the tomato, Lycopersicum esculentum, Mill., and to all or nearly all the other species of Lycopersicum. At times it attacks petunias and even Scrophulariaceous plants, as Anthocersis and Schizanthus. A second species of Peronospora is known on Solanaceous plants, viz., P. Hyoscyami, D.By., a parasite of the common henbane.

In England the disease is generally first seen during the last ten days of July ; its extension is greatly favoured by the warm and showery weather peculiar to that period of the year, and according as the warm and humid weather of autumn is late or early the murrain varies a little in its time of appearance. To the unaided eye the disease is seen as purplish brown or blackish blotches of various sizes, at first on the tips and edges of the leaves, and ultimately upon the leaf-stalks and the larger stems. On gathering the foliage for examination, especially in humid weather, these dark blotches are seen to be putrid, and when the disease takes a bad form the dying leaves give out a highly offensive odour. The fungus, which is chiefly within the leaves and stems, seldom emerges through the firm upper surface of the leaf; it commonly appears as a white bloom or mildew on the circumference of the disease-patches on the under surface. It grows within the tissues from central spots towards an ever-extending circumference, carrying putrescence in its course. As the patches extend in size by the growth of the fungus they at length become confluent, and so the leaves are destroyed and an end is put to one of the chief vital functions of the host plant. On the destruction of the leaves the fungus either descends the stem by the interior or the spores are washed by the rain to the tubers in the ground. In either case the tubers are reached by the fungus or its spores, and so become diseased. The fungus which undoubtedly causes the mischief is very small in size, and under the microscope appears slightly whitish or colourless. The highest powers are lequired to see all parts of the parasite.

The accompanying illustration, drawn from nature, shows the habit and structure of the fungus, Peronospora infestans, Mont. The letters A B show a vertical section through a fragment of a

Peronospora infestans, Mont. —Fungus of Potato Disease.

potato leaf, enlarged 100 diameters ; A is the upper surface line, and B the lower ; the lower surface of the leaf is shown at the top, the better to exhibit the nature of the fungus growths. Between A and B the loose cellular tissue of which the leaf is partly built up is seen in section, and at C the vertical pallisade cells which give firmness to the upper surface of the leaf. Amongst the minute spherical cells within the substance of the leaf numerous transparent threads are shown ; these are the mycelial threads or spawn of the fungus ; wherever they touch the leaf-cells they pierce or break down the tissue, and so set up decomposition, as indicated by the darker shading. The lower surface of the potato leaf is furnished with numerous organs of transpiration or stomata, which are narrow orifices opening into the leaf and from which moisture is transpired in the form of fine vapour. Out of these small openings the fungus threads emerge, as shown at D, D, D. When the threads reach the air they branch in a tree-like manner, and each branch carries one or more ovate reproductive bodies termed "spores" or " conidia," bodies roughly comparable with seeds, as shown at F., E, E. Sometimes other reproductive bodies roughly comparable with the anthers and pistils of flowering plants are borne inside the leaf, stem, or tuber, as at F ; the larger body of these is female, and is termed an "oogonium," and the smaller, which at length pierces the oogonium, is male, and is termed an "antheridium." When the spores or conidia are magnified 400 diameters they are seen as at F', and the contained protoplasm often breaks up into a definite number of parts, as at G. When a spore like F germinates it protrudes an aniceba-like mass of protoplasm, as shown at H, which is capable of reproducing the potato fungus at once ; and when a differentiated conidium as at G germinates it expels about eight minute mobile bodies called "zoospores," each zoospore being furnished with two extremely attenuated vibrating hairs termed "cilia," as shown at J. These zoospores swim about in any film of moisture, and on going to rest take a spherical form, germinate, and produce threads of mycelium as at K ; the mycelium from the germinating conidia or zoospores soon finds its way into the tissues of the potato leaf by the organs of transpiration, and the process of growth already described is re-peated over and over again till the entire potato leaf, or indeed the whole plant, is reduced to putridity.

The oogonium and antheridium as seen at F are further enlarged to 400 diameters at L ; it will here be seen that the smaller male organ or antheridium has projected a fine beak through the walls of the oogonium or female organism; through this beak some of the protoplasm from the antheridium passes into and mingles with the protoplasm of the oogonium ; this is the act of fertilization, and an oospore or resting spore (M, N"), a body roughly comparable with a seed, is the result. After fertilization the oospores quickly drop from their supporting threads and become free like most ripe fruits. As the potato fungus causes the potato to become putrid the mature oospores or resting spores are necessarily confined to the portions of the potato plant which have been destroyed by the fungus, i. e., either to the decayed leaves or stems or to the diseased tubers ; they are brown in colour and generally more or less spinulose or warted. They will not germinate till after a rest of nine, ten, or twelve months, or in some instances even two years. They germinate by protruding threads, which speedily bear spores or conidia as at E, or more rarely zoospores as at J. The resting spores were seen by Dr Rayer and Dr Montague in 1845, and named (in ignorance of their true nature) Artotrogus kydnosporus. The Rev. M. J. Berkeley shortly afterwards identified them as the resting spores of the potato fungus; but they were not seen by any one between the years 1845 and 1875, when in the latter year they were discovered in great abundance and artificially produced from the potato fungus by the writer of this article. At first believed to be rare, they are now known to be amongst the commonest of vegetable productions. The potato fungus is easily made to produce resting spores, and their germination after a year's rest is an observation of no special difficulty. At one time these resting spores were confused by some botanists with a little fugitive transparent fungus, bearing oogonia not half the size of the oogonia of Peronospora infestans, and named Pythium vexans, D. By. ; the latter plant perfects itself in twenty-four hours or at most a day or two, instead of taking a year or more as do the resting spores of the fungus of the potato disease. Pythium vexans has no connexion whatever with the fungus or the potato disease.

The germinating conidia of the potato fungus, as at E, are not only able to pierce the leaves and stems of the potato plant, and so gain an entry to its interior through the epidermis, but they are also able to pierce the bark of the tuber, especially in young examples. It is therefore obvious that, if the tubers are exposed to the air where they are liable to become slightly cracked by the sun, wind, hail, and rain, and injured by small animals and insects, the spores from the leaves will drop on to the tubers, quickly germinate upon the slightly-injured places, end cause the potatoes to become dis-eased. Earthing up therefore prevents these injuries, but where practised to an immoderate extent it materially reduces the pro-duce of tubers. The labour entailed in repeated earthing up is also considered a serious objection to its general adoption.

All diseased potato material should be gathered together and either deeply buried or burnt, as the hibernating germs of the disease (oospores) rest in the decaying potato refuse, and the my-celium itself sometimes hibernates.

[Further Reading] See Berkeley's essay, " On the Potato Disease," in Journal of the Royal Horticultural Society, vol. l., 1S46 ; Professor A. de Bary, "On the Nature of the Potato Fungus," in Journal of Royal Agricultural Society, vol. xii., 1876 ; Earl Cathcart, " The Cultivated Potato," in Journal of Roy. Agr. Soc., 1884 ; J. G. Baker, " The Tuber-hearing Species of Solanum," in Journal of the Linnean Society, vol. xx., 1^84 ; and Worthington G. Smith, Diseases of Field and Garden Crops (1884). In the latter work a full bibliography is given. (W. G. SM.)

The above article was written by: M. T. Masters, M.D., and W. G. Smith.

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