REDUCTION OF CHROMOSOMES 111 
sion does not enter in until the spores are being produced, 
which give rise to the sexual generation (gametophyte). 
This latter has the haploid number of chromosomes in 
its nuclei. We must thus distinguish carefully between 
typical asexual reproduction, where the resulting plant 
is, as it were, but a separated part of the mother plant, 
and the formation of a gametophytic generation from 
the spore produced in the sporophytic generation. In- 
deed each of these generations may have typical asexual 
reproduction leading simply to the formation of other 
plants of the same generation. 
160. After the union of gametes the chromosomes 
from the two gametes remain separate, but usually the 
corresponding chromosomes from each gamete lie close 
together. In the reduction division the chromosomes 
gather at the equator of the spindle as double chromo- 
somes, in all probability representing the two corre- 
sponding chromosomes from the two gametes. Before 
this stage is reached, and while the chromatin matter 
is found on fine 
threads, there is a 
characteristic bunch- 
ing together of these 
threads (called the 
synapsis) in the course 
of which it is sup- 
posed that certain 
characters become ex- 
changed in the corres- 
ponding chromo- 
somes. These double chromosomes split apart and as 
single ones go to the opposite poles. There are thus 
entering into each daughter nucleus only as many chromo- 
somes as were originally present in the gametes. These 
Fig. 49.—Reduction division (diagrammatic). 
