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Uses.- Potatoes are used as human food, stock food, for the manufacture of starch,'syrup, alcohol, dextrin, etc. Potatoes may be preserved as ensilage' for stock feeding, while the pomace' resulting from starch manufacture and potato feed · have received attention for the same purpose. Potatoes may be dessicated, and in this form can be easily preserved in the tropics and arctic regions, and thus furnish an excellent article of diet in a convenient form for transportation. The industry is small at present, but can be readily extended. CHAPTER XVI BREEDING AND SELECTION—PROPAGATION AND

10. S. D. A. Div, of Chemistry, Bul. 58.

U. S. D. A. Farmers' Bul. 79, p. 21. 3 Me. Sta. Report, 1896, p. 28. Bul. 65, p. 115. 4 Vt. Bul. 82, p. 72.

BREEDING

POTATOES are propagated from seed, cuttings, layers of green shoots, sprouts from the eyes of tubers, or portions of the tubers containing a bud or eye. About the beginning of the eighteenth century Shirreff, of England, wrote that “the potato is to be considered a short-lived plant,” and that “the only way to obtain vigorous plants and to insure productive crops is to have frequent recourse to new varieties raised from seed.” Dr. Hunter and T. A. Knight held the same views. T. A. Knight stated that late planting tended to reinvigorate a degenerating variety.' The value of raising new varieties from seed is recognized to-day, and for their production some modern breeders select as parents two varieties, which in most qualities bear close resemblance to each other, avoiding the use of opposites, the claim being that it is easier to fix the type. Others, including Burbank and Garton, make crosses between widely divergent types, although it takes longer to fix the ones they select and there is a lower percentage worthy of a trial. There is, however, more chance of obtaining something above the average. Wide crosses act upon the characters in the plant in a manner similar to a vigorous push on the pendulum of a clock—it goes higher on each side: plants of higher value and plants of lower value than either parent are secured. A plant of high value is secured and grown for a period of years in order to fix it. Those who have regarded the valuable characters which led to the selection of the individual as fixtures from the beginning claim that this period of fixing is solely for the purpose of elimination of the undesirable characters, and that it ought to be termed “the elimination period” rather than “the fixing period.” The interrelationship of different qualities is not well known, but it has been . noted that a variety having a few thick stalks yields large tubers, but few in number, while a number of weak stalks is often found with a number of small tubers. Early ripening and resistance to blight or rot (Phytophthora infestans) are not generally found together. It is claimed that a large production of seedballs goes hand in hand with a small production of tubers. T. A. Knight claimed that varieties which did not bloom readily could be induced to do so by removal of the soil from round the tuber-bearing stems, the explanation offered being that the plant's failure in tuber production would stimulate the production of seed.

1 Miller's “Gardeners' Dictionary,” ed. 1807, “Potatoes,” and Don's “Gardeners' Dictionary,” 1831–38, Vol. IV., pp. 400-406.

In pollenizing varieties artificially the stamens should be removed from the female parent with fine pincers just as the bloom opens, or before, and the flower enclosed in a paper or gauze bag. The proper time to apply the pollen is known by the moist appearance of the stigma. The pollen from the desired variety should be dusted on the stigma on two or three successive days. The bag may be removed when the stigma dies

1 Philosophical Transactions, 1806.

and the bloom withers. The fruit, or seed-ball, may contain from 100 to 300 seeds. These are washed from the ripe seed-balls, dried, and at the proper season sown under glass, or in a hot-bed, or out-of-doors in

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FIG. 50—POTATO FLOWER, WITH CALYX AND COROLLA REMOVED On the left are shown the anthers closed round the pistil. On the right the anthers are expanded, pistil not shown The inner surfaces of the anthers show the line where rupture occurs when the pollen is liberated. Gener

ally this occurs only near the upper portion of the anther.

flats. The seeds germinate rapidly. Later they are transplanted to a well-prepared piece of land outside. The distance apart varies with different growers—from 12 X 12 to 26 x 26 inches, and sometimes more. The upright stem bears leaves and the axils of the first leaves bear shoots, which turn downward into the ground and bear tubers. The old idea that the first year's

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crop consist of small tubers, the next larger, and so on, does not always hold, as a tuber weighing over seven ounces has been produced the first year. The Burbank potato was full size the first year it was grown from seed, and many breeders feel that unless the tubers are of edible size the first year they are not likely to be worth further care. Frequently the tubers do not reach full size until the second year. The tubers from each plant must be kept separate, the best selected

FIG. 51 – PISTIL OF POTATO and planted again. The

FLOWER, SHOWING THE PARTS distance apart varies be- a-Stigma, where pollen is applied. tween 26 x 12 and 40 x 6–Style, down which the pollen tube

goes to the ovary, c, where it fertilizes 40 inches. Wider plant- the ovule, which become the seeds (see ing permits the study of Fig. 3). d— Attachment of stamens,

- removed to prevent self-fertilization. the individual. The

e-Petals, partly torn away to expose third, fourth, and fifth ovary. f-Sectional view of calyx. year field culture is given, and a variety may be found worthy of a name and further trial before distribution. The breeder's aim is to produce varieties which excel in productivity, power to resist diseases, earliness, quality, percentage

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1 Minn. Bul. 87, p. 10.

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