430 THE AMERICAN NATURALIST [Vol. XLIV 



character pairs are the ones affected when a somatic 

 mutation or bud variation occurs in asexual reproduc- 

 tion. Simple loss of the factor takes place. Segrega- 

 tion, therefore, takes place at other times than the 

 reduction of the chromosomes. 



In a previous paper, 4 the writer analyzed the data 

 then extant concerning the hypothesis of degeneration 

 or "running out" of potato varieties. The conclusion 

 was that no degeneration due to continued asexual prop- 

 agation occurs. No data have been obtained which re- 

 fute this view, but the study of progeny of selfed potato 

 varieties has suggested an explanation of a certain 

 amount of diminution in yield after long-continued 

 asexual propagation. All commercial potato varieties 

 which have been selfed and their progeny grown, have 

 proved to be heterozygous in at least two characters. 

 It has been shown 5 that when maize biotypes are 

 crossed, the F 1 generation has greater vigor and gives 

 larger yields than the parents. It is a condition apart 

 from inheritance, and is probably due to the heterozy- 

 gous condition of certain characters in the germ cells. 

 It may be correlated with the actual mechanical opera- 

 tion of segregation. Since potato varieties are retained 

 in cultivation on the basis of yield and since those on 

 the market have been found to be heterozygous in many 

 of their characters, probably the same phenomenon is the 

 cause. May there not be a gradual loss of the stimulus 

 due to crossing through continued bud propagation, 

 so that the variety has only the vigor of one homozygous 

 in the same characters? The variety of course remains 

 heterozygous for those characters in which it was orig- 

 inally heterozygous, yet there may be a gradual decline 

 of the stimulus to cell division than it once possessed. 



4 A "Study of the Factors influencing the Improvement of the Potato," 

 Bull. 111. Agr. Exp. Sta.. No. 127, 375-456, 1908. 



"East, E. M., "The Distinction between Development and Heredity in 

 Inbreeding," Ameb. Nat., 43: 173-181, 1909. 



