142 



Tilt: AMERICAN NATURALIST [Vol. LI 



distribution parallels the facts. In each instance the 

 negative variant— may we call it the recessive— breeds 

 true. In one case the positive variant breeds true, in the 

 other case it gives a simple Mendelian ratio. 



The mechanism necessary for such phenomena is not 

 difficult to picture. Bud-variations are many times more 

 frequent in hybrids, that is, in plants heterozygous for 

 one or more characters, than they are in pure species. 

 This is the view of Cramer, this was the view of Masters, 

 the eminent English student of bud-variations and tera- 

 tological phenomena, this was the conclusion drawn by 

 the present writer in several articles published some 

 years ago. Such results would be obtained either when 

 the proper germinal change occurs in the chromosome 

 whose mate lacks a character for which the plant is hetero- 

 zygous ; or, when there is a dichotomy in which the chro- 

 mosomes of such a pair are not halved but pass the 

 material basis necessary for the production of the posi- 

 tive character to one daughter cell and not to the other, 

 provided the daughter cell lacking the character gives 

 rise to a branch. 



A bud-variation in a character for which the plant was 

 homozygous would be obtained only when simultaneous 

 like clianges occur in both chromosomes of a homologous 

 pair, or when the material basis necessary for the pro- 

 iluction of the positive character all passes to one daugh- 

 ter cell, as described above. 



This liyi^otliosis would account for the fact that hetero- 

 zygote> l i-c to biid-variations more frequently than 

 ho7iioz\ ii()tr>. -iiirt' ;i <>-orTniiial ehanu-e seldom gives rise 



