22 BULLETIN" 195, IT. S. DEPARTMENT OF AGRICULTURE. 
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 all observant potato growers that there is a great 
variation in the number of tubers produced by 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 6 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 uniformit} 7- 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 
qualities are as follows : 
(1) Disease resistance of vine. 
(2) Drought resistance of vine. 
(3) Heat resistance of vine. 
(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 
suffice 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- 
bilities have not been unrecognized by earlier investigators is self- 
evident from the few examples which are cited on the following pages. 
EARLY SELECTION EXPERIMENTS. 
One of the earliest 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, 1 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 
i Hallet, F. P. Food-plant improvement. In Nature, v. 26, no. 656, p. 91-94, 1882. (See p. 92.) 
