CHROMOMERES 269 
tween the two chromosomes, except that, of course, the 
two members of the same pair of allelomorphs would 
never coexist in the same chromosome. Since the 
‘two chromosomes of a pair pass into different germ- 
cells, precisely that chance distribution of allelomorphs 
which is required on the Mendelian theory would thus 
be arrived at. 
De Vries’ explanation throws light on one pheno- 
menon which is not accounted for on the supposition 
that each chromosome represents a separate allelo- 
morph. In the diagrams previously given of the 
behaviour of Mendelian characters within the cells we 
have given no indication of a conjugation in pairs 
previous to the reducing division. Such a process of 
fusion is, however, one of the most marked phenomena 
in the behaviour of the chromosomes at the parallel 
stage of their existence. On the chromosome-allelo- 
morph view, the phenomenon of mitosis as bringing 
about an equal division of hereditary particles between 
the cells, and the process of reduction in the number 
of the chromosomes, are both accounted for, but there 
is no explanation of the fusion between the pairs of 
chromosomes. On de Vries’ view, however, this pro- 
cess is necessary in order to bring about the necessary 
redistribution of allelomorphs between the chromo- 
somes, and so between the germ-cells into which the 
latter pass. 
In cases where the phenomenon of correlation or 
coupling has been observed we must suppose that there 
is some mechanism which causes the representative 
