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toes are classified into early, medium or second early, and late varieties, according to the time they take to reach maturity. Early varieties may mature in 70 to
FIG. 22—THE IMPORTANCE OF HAVING UPRIGHT HAULM AND PRESERVING THE FOLIAGE IS NOT SUFFICIENTLY APPRECIATED) Plant photographed early in September, 1904, when many others near were dead (C. U. Farm). Upright haulm facilitates late cultivation and spraying. The foliage dries quickly, and then is not so favorable for the growth
of spores of rot.
90 days after planting ; second earlies, in 90 to 130 days, while late varieties may continue to grow for 200 days.
9. The haulm. The haulm and leaf are receiving more attention to-day than formerly. The size of haulm has an influence upon the distance apart of planting. Large haulm is more trouble to spray, re
quiring more solution, and it is always lying over the ground when the last spraying ought to be given, and is in the way at lifting-time, whether the potatoes are raised by hand or digger. Modern breeders aim to produce a short haulmed, upright, heavily leaved top, because the upright habit of growth (Fig. 22) is more likely to keep clear of disease than a spreading habit, owing to water being shed from the former more readily than from the latter, and not offering a foothold to the disease spores (Fig. 37). Plants whose branches lie on the ground are more liable to disease because they cover a greater area, their leaves, touching the ground, are almost always damp from contact with it, and sun and wind cannot so readily reach them. Very tall haulmed varieties are readily beaten down by storm and wind, and in this state they cannot dry so readily; hence, they fall in a clammy mass, very favorable for the growth of disease spores.
Varieties with strong, hardy haulm suffer less from spring frosts. Late varieties usually have taller haulm than first early varieties. Some varieties make their heaviest growth of foliage late in the season, and in this way are not so subject to attacks of early blight.
10. The leaf. The British disease-resisting varieties have hard, thick leaves. Whether the thickness of the leaf is an important factor in their resistance to rot (Phytophthora infestans) is not determined. The fact that spraying the upper surface of the leaf tends to prevent blight would seem to show that access to the inside of the leaf is obtained by growth through the cell walls as well as through the stomata, on its under surface. If this be true, then the thickening and hardening of the cuticle and the palisade cells (Fig. 34), or thick cells on the upper surface of the leaf, will no doubt prevent many spores from reaching the inside cells of the leaf. They may germinate on the surface, but not enter, unless they find some place where the leaf has been injured. The punctures of the fleabeetles are, on this account, of great importance, as they furnish an entrance to the inner cells (Fig. 40).
N. A. Cobb, of Australia, has shown that in the case of wheat the varieties most resistant to rust (Puccinia graminis and P. rubigo vera), none being absolutely resistant, have narrow, stiff, upright foliage, while those most liable to attacks have broad, flabby, and pendant foliage. In the plants resistant to rust the cuticle of the leaf is much thicker than in the others, and is so thick that the rust spores, when they germinate on the outside of the leaf, cannot penetrate it, or if they do succeed in entering the leaf through stomata, the threadlike growths of the parasite cannot rupture the cuticle wall to fructify; and, further, some wheats have stomata so narrow and are so well covered with wax that the germinating threads of the rust spore fail to enter every time. These circumstances seem to support the claim that the tough, thickwalled, hard, dry leaf is the one to select for diseaseresistant powers. It has been observed that plants of the potato family having this type of leaf are fairly free from fungus leaf diseases. It is essential that the leaves of the potato be abundant to insure a good yield.
11. The vigor of the variety. Vigor is the power stored in a plant which enables it to overcome difficulties at different periods of growth, A variety must
have vigor. If not, it may fail to establish itself during the early part of its career, being a shy budder; it may be readily injured by frost, heat or cold, drouth or a wet period, and, having little recuperative power, will give small returns for the labor bestowed upon it. If it survives to tuber-formation time it will probably fail then. Plants or varieties showing lack of vigor must be discarded. Some varieties have short staying power; they appear to be vigorous for one or two years, and then suddenly collapse. Others have great staying power--as, Early Rose, which has been prominent for over forty years.
The stateinent is sometimes made that modern varieties are not so long-lived as their ancestors—that they are deficient in staying power. If the statement were true, it might be explained by saying that new varieties are produced more frequently, and that on account of their heavier yielding power or better quality they displace the old ones. The facts seem to show that modern potato breeders have more than maintained vigor and staying power. Hays, of Minnesota, and others, place the life of a good modern variety at about thirty years. This seems to be accepted by many, both here and abroad. Dr. Hunter, of England, in his “ Geological Essays," i writing about one hundred years ago, states “that varieties continue in vigor about fourteen years, after which the produce gradually declines.” Shirreff and T. A. Knight held similar views; the latter wrote that “not a single healthy
1 “Geological Essays,"' Exp. 14, p. 348.
? Hort. Trans., Vol. I., and Miller's “Gardeners' Dictionary," ed. 1807, “ Potatoes,"
plant of any sort of potato that yields berries, and which was in culture twenty years ago, can now be produced.” So late as 1838 this idea was accepted by the horticulturists of England. It is interesting to note that the average yield of potatoes in England a hundred years ago is stated to vary between 185 and 300 bushels, and sometimes 440 bushels, per acre. The average yield to-day is about 230 bushels, but some growers produce 750 bushels per acre frequently. The average improvement in the quality of the tubers is greater than the average improvement in yield. Formerly the potatoes were grown largely for stock, and were of poor flavor and bad cooking quality.
Some new varieties make vigorous growth, and, becoming bark-bound, the skin cracks. Such varieties are regarded as of coarse and inferior quality, and lacking in appearance. This character may be eliminated by judicious selection. Deficiency in vigor is indicated by the formation of misshapen tubers drawn out at either end, the presence of second growth, weak buds, lack of uniformity in texture—as, hardness at the ends of the tubers when cut, especially brittleness of texture. Tubers showing any such characteristics should not be planted..
When potatoes are planted 15 inches apart in 36inch rows, there are 11,616 plants per acre. If each plant had sufficient vigor to yield three tubers, each weighing half a pound, or four weighing six ounces each, a yield of 290 bushels of salable potatoes per acre is assured. No one can afford to use seed of less vigor than this. I Don's“Gardeners' Dictionary," 1838, Vol. IV., pp. 400-406.