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 process 

 is necessary in order to bring about the necessary redis- 

 tribution of allelomorphs between the chromosomes, and 

 so between the germ-cells into which the latter pass. 



[More recently Professor T. H. Morgan has brought 

 forward a much more complete theory of the relation 

 between chromomeres and Mendelian characters, based 

 on the behaviour of characters which show gametic 



