Sept. 1, 1920 Line-Selection Work with Potatoes 545 



plant appeared with white potatoes. This means that one eye from a 

 typical Blue Victor tuber produced a plant which bore white potatoes 

 while all other eyes from the same tuber produced plants with blue 

 potatoes true to type. This hill of white potatoes will, if planted, give 

 plants bearing only white potatoes, for these simple bud sports or simple 

 vegetative mutants may be perpetuated by propagation from vegetative 

 parts. Here, then, we have an excellent example of how new varieties 

 appear by mutation, but apparently such bud sports do not appear 

 frequently. 



If we purpose to champion the cause of selection within potato clons 

 we must either show that high-yielding mutants, less striking than the 

 one just mentioned and possibly for this reason more often unobserved, 

 frequently appear within the clon and form the basis for selection, or we 

 must break down, so far as clonal varieties are concerned, the theory 

 that all fluctuations, or modifications are nonheritable. The greater 

 part of the data here presented is the result of work begun with the 

 intent of throwing light upon the first question. Experiments are also 

 under way bearing upon the heritability of fluctuations, but as yet the 

 data are not sufficient to warrant publication. 



No one, I think, will doubt the value of certain lines of potato seed- 

 selection work. For instance, there is abundant evidence to show that 

 under anything like favorable environmental conditions the yielding 

 power of a variety may be maintained by careful selection. In other 

 words, a system of seed-tuber production which aims at the annual 

 elimination of diseased or degenerate hills will, except under the most 

 unfavorable environmental conditions, maintain a high-yielding popu- 

 lation of any variety. But aside from the elimination of these weak 

 hills we may question whether any practical results will come from fur- 

 ther effort. In this case we are eliminating the hills that are below the 

 average in vigor, the loss of vigor being due to attacks of disease or to 

 degeneration. A very satisfactory method of procedure in such selec- 

 tion efforts is well outlined in Circular 73 of this Station.^ The extent to 

 which yields are increased by such selection is largely determined by 

 the stock started with, its susceptibility to disease, and the tendency of 

 the particular variety to degeneration under existing climatic and soil 

 conditions. Starting with a variety population containing a large per- 

 centage of degenerate or diseased plants, proper selection will bring 

 about a marked increase in yield. In growing a variety that has degener- 

 rate tendencies under certain environmental conditions, such a system 

 of selection will be found very helpful in maintaining the jdelding power 

 of the variety. For the purpose of illustration, some examples may 

 be cited. Russet Burbank, as it has been grown at Bozeman, is a very 

 stable variety. Very few diseased hills appear in the plots, and very 



1 Whipple, O. B.. a seed plot method of potato improvement. Mont. Agr. Exp. Sta. Circ. 73, p. 

 71-73. 1917. 



