Mar. *4,1923 
Permanence of Variety in the Potato 
949 
apparently used a commercial stock. East found no difference in yield 
between the progeny of high and low-yielding hills in stock which was 
obtained from a single tuber of the Rural New Yorker variety. He 
believes that great caution should be exercised in recommending asexual 
selection to commercial growers as a means of actual improvement of the 
crop, in view of the facts that of many investigations on the point no 
indisputable evidence of improvement has been reported and that even 
the questionable instances of positive results are extremely rare. 
Stuart (21) reported in 1915 the results obtained in some rather exten¬ 
sive studies on the value of the tuber-unit and hill-selection methods as 
a means of potato improvement. Remarkable dissimilarities were found 
between individuals under both the tuber-unit and the hill-selection 
methods. Stuart did not attempt to explain the cause of the differences 
further than to point out that in certain instances— 
other causes than that of inherent unproductiveness must have operated to lower the 
yield, 
and states— 
that the tuber unit method and hill selection method of improvement are chiefly 
valuable in pointing out the weak, unproductive, and diseased tuber. 
Stewart (20) in his observations on some degenerate strains of potatoes 
states that— 
it is doubtful if any method of seed selection will prevent the “running-out" of seed 
potatoes under certain conditions. 
In a recent article Whipple (27) has published the results of five years' 
work in pure-line selection. He calls attention to the persistency with 
which degenerate types (curly-dwarf) appear in pure lines and the con¬ 
sequent difficulty of interpreting yield data. Similar experiences have 
been recorded by Wellington (26) in a paper in which he points out the 
uselessness of hill selection under conditions where rapid deterioration or 
running-out is prevalent. The deterioration mentioned by Wellington 
was expressed by the production of the so-called “curly-dwarf” type of 
plants. This was later found by Krantz and Bisby (ji) to be due to a 
disease very similar in its nature to mosaic and is probably nothing more 
than a severe expression of this disease. 
A few experiments have been conducted to test the effect of asexual 
selection on characters other than yield. The results of a carefully con¬ 
ducted experiment for the purpose of determining the effect of selection 
for high and low nitrogen content was reported by East (5) in 1910. No 
difference in nitrogen content was found during three years of continuous 
selection. In conclusion East says— 
that neither the relative content of dry matter nor that of nitrogenous matters of the 
potato can be changed by the selection of fluctuations. 
In attempting to isolate a blight-resistant strain of potatoes Stuart (21) 
obtained indifferent results. After selecting for three yearn to improve 
the form 'of the White McCormick variety, White (28) concluded that 
no improvement could be secured in this variety through selection. As 
previously mentioned, Stewart (20) and Wellington (26) were unsuccessful 
in trying to isolate a strain of potatoes resistant to factors causing degen¬ 
eracy. 
The evidence presented does not offer much encouragement to the 
plant breeder for the use of asexual selection for improving the potato. 
The opportunity that the mechanism of sexual reproduction offers for 
