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; 
Fic. 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- 
