CYTOLOGICAL INVESTIGATIONS IN PLANT HYBRIDS. 291 
Hieracium of Mr. Ostenfeld, especially one hybrid, which Mr. Ostenfeld 
had obtained by crossing H. excellens with H. Pilosella. 
I examined some forms of this hybrid and found that they had a 
different number of chromosomes. 
This depends upon the fact that the ege-cells in H. excellens differ 
greatly in their number of chromosomes. Some have fifteen, sixteen, 
seventeen, twenty, and soon. And this also depends upon the fact that 
the Reduction-division is irregular, resembling the facts I have found in 
Drosera. I cannot go further into detail, but I have followed step by step 
the development of the embryo-sacs, and have found that egg-cells really 
have different numbers of chromosomes. 
If these egg-cells are conjugated with a male gamete from a species 
with a fixed number of chromosomes, as in that case, there must be different 
results, or, in other words, the plants produced from these egg-cells con- 
tain very different chromatin material, and thereby the differences in these 
forms may perhaps be explained. Of this, however, I will not say that 
this explanation has a general bearing. But it seems to me that this 
case indicates the necessity for a close co-operation between the cytologist 
and those who are experimenting on the question of heredity. 
