230) 
A TEXTBOOK OF GENERAL BOTANY 
not found in ordinary nuclear divisions. During this stage the 
chromosomes become joined together in pairs. 
As a result of this the chromosomes, instead of taking their 
places on the spindle singly, do so in pairs. In all other 

Fia. 231. Diagrammatic representation of the 
behavior of chromosomes during fertilization 
and reduction 
For convenience in tracing the history of the 
chromosomes, those from the male nucleus are 
shaded, Above is the union of male and female 
nuclei to form the fertilized egg; lower left, di- 
vision of fertilized egg; lower center, union of 
chromosomes from the male and egg nuclei in 
pairs in prophase of reduction division; lower 
right, the constituents of the pairs of chromosomes 
have separated at metaphase of reduction division 
divisions each chro- 
mosome splits longi- 
tudinally; but during 
this division, instead 
of each chromosome’s 
splitting, the members 
of each pair separate, so 
that only half as many 
chromosomes pass to 
the poles in the ana- 
phase of this division 
as in the preceding 
division. 
The different chro- 
mosomes are believed 
to carry different he- 
reditary factors, and 
in some cases the in- 
dividual chromosomes 
can be distinguished 
from each other by 
differences in size and 
shape. The chromo- 
somes in the male nu- 
cleus appear to differ 
from each other, while 
the complete set in 
the male nucleus is 
apparently similar to the complete set in the egg nucleus. The 
fertilized egg thus has two complete sets of chromosomes. 
When two chromosomes unite in the prophase of the hetero- 
typic division, these seem to be not dissimilar but similar 
