22 BULLETIN 195, U. S. DEPARTMEN'T OF AGRICULTUEE. 



within most of our cultivated varieties. This is particularly true 

 with respect to uniformity in shape and size. In addition to this, it is 

 well known to aU observant potato growers that there is a great 

 variation in the number of tubers produced b}'^ individual plants. 

 Some plants produce 2 or 3 large tubers, with no small ones; others 

 the same number of large tubers, but with a half dozen or more small 

 ones; while others may be found producing from G to 10 or more 

 medium-sized merchantable tubers and practically no small ones. 

 It is clearly evident that the latter plant is the most desirable, pro- 

 vided that it has the power of reproducing this character. Probably 

 very few plants have a productive capacity in excess of the average 

 optimum expression of the variety. The abnormal yield is generally 

 due to one or more of several causes, such as a larger or more vigorous 

 seed piece, a slightly greater supply of plant food or moisture, or both, 

 minimum injury from insect pests and fungous diseases, or any other 

 favorable condition which enables that particular plant to reach or 

 exceed the optimum or normal production of the variety. Failure 

 to take these factors into consideration may lead the selectionist to 

 interpret his results erroneously or to be unduly elated or depressed 

 over the behavior of his selections in the first and second years of 

 their isolation. 



In addition to productiveness and uniformity in shape and size, 

 there may be still other qualities which it is possible to secure 

 through intelligent selection. Some of the more important of these 

 quahties are as follows: 



(1) Disease resistance of \T.ne. 



(2) Drought resistance of vine. 



(3) Heat resistance of \ine. 



(4) Vigor of plant. 



(5) Greater adaptability to peculiar environmental conditions of soil or climate. 



Undoubtedly other objects of selection could be mentioned, such as 

 tubers with shallower or less numerous eyes; but the foregoing may 

 sufhce to show the possibilities for selective work in the improvement 

 of the potato. That the subject is not a new one and that its possi- 

 bihties have not been unrecognized by earher investigators is self- 

 evident from the few examples which are cited on the following pages. 



EARLY SELECTION EXPERIMENTS. 



One of the earhest recorded experiments in which a definite effort 

 was put forth to increase the productive capacity of the potato plant 

 was that carried on from 1868 to 1882 by Hallet,^ who reports as 

 follows : 



In the case of the potato, I have also applied my system, starting every year with a 

 single tuber, the best of the year (proved to have been so by its having been found to 



1 Hallet, F. P. Food-plant improvement. In Nature, v. 26, no. 656, p. 91-94, 1882. (See p. 92.) 



