. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. BUD SELECTION 395 or 4 years and found 12 bud mutations. Changes were noted in the color, shape and habit of growth of the tubers and in the depth of the eyes. But as for the bearing of bud mutations on origin of new varieties East reached tlie conclusion that, while isolated cases of improvement might be due to selection of bud mutations, yet comparatively few (probably less than per cent.) of our present varieties arose in this manner. This evidence on the origin of varieties has led East to
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. BUD SELECTION 395 or 4 years and found 12 bud mutations. Changes were noted in the color, shape and habit of growth of the tubers and in the depth of the eyes. But as for the bearing of bud mutations on origin of new varieties East reached tlie conclusion that, while isolated cases of improvement might be due to selection of bud mutations, yet comparatively few (probably less than per cent.) of our present varieties arose in this manner. This evidence on the origin of varieties has led East to adopt the view that probably all bud mutations are so exceedingly rare in the potato that few, if any, cases of "running-out" or "degeneration" in varieties are to be explained on this basis. He believes the principal factor in such dete- rioration is disease, and that in numerous experiments on potatoes, in. Fig. 162.—Variation in yield between tuber-units from the same hill. Above, the progeny of two tubers from hill selection No. ; below, that from hill selection No. 4. (After Stuarl.) which it is shown that successive selections have raised the average yield over that of the unselected tubers, the results are entirely due to the elimination of diseased tubers. While the ehmination of chseased tubers or of tubers that were weak- ened by disease in the leaves or stem does undoubtedly explain the success of many selection experiments it may not account for all of them. Tests of individual tubers of almost any commercial variety apparently reveal inherent differences in the tubers. Although the plant is very susceptible to environmental conditions and some tuber characters such as shape and size are very unstable, yet sometimes the product of two closely similar tubers wliich came from the same hill when grown under closelj^ similar conditions will differ widely (see Fig. 162). The most satisfactory method of testing individual tubers is the tuber-unit
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