134 SEX INHERITANCE 
in the cells of the sporophyte generation (diploid). 
In the female gametophyte (haploid) the larger 
member of the pair is present, and in the male 
gametophyte (haploid) its smaller mate. At the 
reduction division in the sporophyte, when four 
spores are formed, two of the spores in each tetrad 
contain each a large chromosome and two a small 
one. It is fairly well determined that from each 
set of four spores, two give rise to female plants of 
the gametophyte generation, and two to male 
plants. In this case the males and females are 
plants with the haploid number of chromosomes, 
one with the large chromosome and the other with 
the small one. The sporophyte being diploid con- 
tains both chromosomes, which, as stated, are 
separated again when the spores are formed, 1.e., 
at a time corresponding, it would seem, to the 
maturation division of the egg and the sperm. 
_It may be recalled in this connection that the 
male bee and the male Hydatina are haploid organ- 
isms; but in them, unlike the haploid gametophyte 
generation of the liverworts and mosses, modified 
maturation divisions occur. By means of altera- 
tions in the maturation divisions female-producing 
gametes only are produced. 
SEX-RATIOS 
Both the XX-XY and the WZ-ZZ types give 
equal numbers of males and females, provided that 
both kinds of gametes are equally viable, that 
