POTATO IMPROVEMENT 



233 



practical breeder to discard "clonal selection" as one means of 

 obtaining high yields, for it is a recognized fact that seed plot 

 methods are of much practical importance. The results, how- 

 ever, are probably not due to the isolation of bud mutations but 

 rather to the use of tubers which have developed normally and 

 which furnish the right conditions to give the resultant plants 

 a favorable start. May not the conditions be much the same 

 as with any vegetatively propagated plant. Bonnier, for 

 example, found that about three years are required before a low- 



FIG. 58. Tubers produced under such a cheesecloth cover have given good 

 yields during the seasons 1918 and 1919 while tubers from uncovered vines 

 produced very inferior yields. University Farm, St. Paul, Minnesota. (Cour- 

 tesy of Krantz.) 



land dandelion transported to alpine conditions fully expresses 

 the characters of a dandelion plant which had been grown under 

 these conditions for many years. On returning the same plant 

 to the lowlands about the same number of years elapsed before 

 the. plant had again fully attained the lowland habit. This is 

 probably not a germinal change but the normal expression of the 

 plant under a particular environment. With the clonally 

 propagated potato there is a cumulative response to unfavorable 

 conditions. Such conditions modify the plant's development 

 and therefore influence the development of the following year's 

 crop. There seems no reason for believing that an actual ger- 

 minal mutation has occurred. 



