52 PHARMACEUTICAL BOTANY 
In the first division called heterotypic mitosis, the resultant cells 
contain, in their two daughter nuclei, only one-half the number 
of chromosomes found in the nuclei of the body cells. ‘These 
nuclei do not pass into the resting condition but soon undergo a 
second division. 
In the second division called homotypic mitosis, each of the two 
nuclei divide again to form an aggregation of four daughter cells 
in all, each with a nucleus containing the x number of chromo- 
somes. The x number of chromosomes continues through the 
whole gametophyte generation, so that the uniting egg nucleus 
and sperm nucleus possess this number. In the act of fertiliza- 
tion the x chromosomes from the egg nucleus are combined with 
the x chromosomes from the sperm nucleus to form 2x (diploid) 
chromosomes in the zygote. When the zygote divides, each of 
its daughter cells contains 2x (diploid) chromosomes and their 
number is continued throughout the sporophyte generation. 
