May, 1905.] The Nature of the Reduction Division. 
339 
As stated above, Mendel’s law can be explained on the theory 
of pure sex cells. In working out the peculiar activities of the 
chromatin during cell division, cytologists have come to look 
upon the chromosomes as special bearers of hereditary tendencies 
although other parts of the protoplasm may also have something 
to do with the transmission of heredity. Now if a transverse 
division occurs and the chromosomes are pure the daughter 
nuclei could then be organized as pure having only chromosomes 
derived from the egg or sperm (Fig. 5, a-b). No difference how 
many subsequent, longitudinal splittings take place before the 
formation of gametes, the gametes would always be pure cells. 
Fig. 
a t) 
5. Diagram of transverse division 
pure and mixed cells. 
showing possible production of 
In conjugation there is twice the chance for a mixed oospore to 
be formed as a pure one and hence the splitting of the ht^brid 
race in the proportions given by Mendel’s law. But suppose 
that the chromosomes were joined in pairs and arranged in the 
mother star in such a way that half of the male chromosomes 
were on one side and half on the other and the same 
for the female chromosomes then the transverse splitting 
would always result in mixed cells and no splitting of the race 
could occur (Fig. 5, c-d). The daughter nuclei would be mixed 
even if the chromosomes making up the pair were pure. Other 
arrangements are possible, and in case the chromosomes are not 
reorganized as pure bodies the cells resulting from reduction 
could of course not be pure. But whatever the facts may be it 
appears that all cases of hybrids that follow Mendel’s law as well 
as those which do not can be accounted for on the theory of pure 
chromosomes and a qualitative reduction division. This would 
not prove however that the chromosomes are organized as pure 
bodies or that there is a transverse splitting of chromosomes. 
These facts must be worked out from a study of nuclear division, 
and this is the important and difficult problem to be solved. 
Anyone can compare the results of cytology and plant and ani- 
- mal breeding after the facts have been ascertained. But to work 
