New York Agricultural Experiment Station. 427 



Keeble and Pellew (20) in their study of the mode of in- 

 heritance of stature in peas found that the first generation crosses 

 between the half-dwarf varieties Autocrat and Bountiful greatly 

 surpassed either parent in height. Since one variety possessed a 

 thick stem and the other long internodes, the authors came to 

 the conclusion that both of these factors were requisite for the 

 production of maximum growth in the pea. The explanation is 

 best given in their own words : " The suggestion may be hazarded 

 that the greater height and vigor which the first generation of hy- 

 brids commonly exhibit may be due to the meeting in the zygote 

 of dominant growth-factors of more than one allelomorphic 

 pair, one (or more) provided by the gametes of one parent, the 

 other (or others) by the gametes of the other parents." This 

 hypothesis was supported by a close approximation to the 9 :3 :3 :1 

 ratio which signifies the presence of two allelomorphic pairs. 



An older hypothesis to explain the increase in vigor, which does 

 not essentially disagree with that of Keeble and Pellew, is one 

 postulated by G. H. Sliull (31). He writes: " In 1908, I sug- 

 gested a hypothesis to explain the apparent deterioration attend- 

 ant upon self-fertilization by pointing out that in plants, such as 

 maize, which show superiority as a result of cross-fertilization, 

 this superiority is of the same nature as that so generally met with 

 in Fi hybrids. I assumed that the vigor in such cases is due to the 

 presence of heterozygous elements in the hybrids, and that the 

 degree of vigor is correlated with the number of characters in re- 

 spect to which the hybrids are heterozygous. I do not believe 

 that this correlation is perfect, of course, but approximate, as it is 

 readily conceivable that even though the general principle should 

 be correct, heterozygosis in some elements may be without effect 

 upon vigor, or even depressing. The presence of unpaired genes, 

 or the presence of unlike or unequal paired genes, was assumed 

 to produce the greater functional activity upon which larger size 

 and greater efficiency depend. This idea has been elaborated by 

 Dr. E. M. East and sho"\\Ti to agree with his own extensive experi- 

 ments in self-fertilizing and crossing maize. He suggested that 



