AND MENDEL'S LAW 267 



omatic and reducing divisions respectively, can 

 scarcely fail to be struck by the extraordinary simi- 

 larity between the two processes. It seems quite 

 clear that there must be some real connection between 

 the behaviour of chromosomes as seen microscopically 

 on the one hand, and the behaviour of allelomorphic 

 characters as deduced from the results of experiment 

 on the other ; and that the evidence derived from these 

 two forms of study is bound to be of considerable 

 mutual benefit. 



At first sight it might be thought that the chromo- 

 somes are the actual bearers of Mendelian characters, 

 in the sense that each chromosome represents a single 

 allelomorph ; and, indeed, there is no fundamental 

 difference between the behaviour of chromosomes and 

 that of our supposed character-bearing particles. But 

 there is, at least in some cases, a fatal objection to 

 this belief in the fact that in certain plants the number 

 of separate allelomorphic pairs which may be born by 

 a hybrid is greater than the reduced number of chromo- 

 somes which the germ-cells of this hybrid contain. 

 For instance, in the case of the pea the reduced 

 number of chromosomes is seven, and Mendel himself 

 described the behaviour of seven independent pairs of 

 allelomorphs in peas. Recent study has revealed the 

 presence of at least four additional pairs of allelo- 

 morphs in these plants, all of which are probably equally 

 independent of one another. 



We must, therefore, seek a different explanation, 

 and de Vries has recently suggested one which up to 



