268 RECENT CYTOLOGY 



the present time appears the most likely to represent 

 the true account of the phenomena. De Vries' ex- 

 planation is associated with the finer structure of the 

 chromosomes themselves, a subject upon which we 

 have not hitherto entered. Under high powers of the 

 microscope, and after very careful preparation, it is 

 possible to observe that each chromosome contains a 

 number of separate darkly-staining granules which are 

 known as chromomeres. When the pairs of parental 

 chromosomes fuse together previous to the reducing 

 division, the chromomeres which they contain appear 

 to meet together in corresponding pairs. The members 

 of each pair fuse together completely, afterwards 

 separating as the chromosomes separate; 



FIG. 46. 



De Vries supposes the Mendelian allelomorphs to 

 be contained in the chromomeres, and that when these 

 granules fuse together an exchange of allelomorphs 

 takes place between the chromosomes. This ex- 

 change proceeds in such a way that when the chromo- 

 somes separate after fusion, it is a matter of simple 

 chance whether a particular allelomorph has remained 

 in the chromomere which originally contained it, or 

 has passed over into the other member of the pair. 

 Thus, in a sufficient number of cases we should get 

 all possible chance distributions of allelomorphs be- 



