212 PLANT LIFE 
CHAPTER XIX 
SEXUAL REPRODUCTION 
SEXUAL reproduction occurs in almost all 
the divisions of the animal and vegetable 
kingdoms, although it has not as yet been 
detected in some of the lower groups. These 
consist either of organisms of extreme sim- 
plicity, or of those in which we have grounds 
for believing that sexuality has been lost, 
probably in connection with special conditions 
of nutrition. In some of the higher plants 
the sexual function has degenerated, though 
we cannot clearly trace the loss to any definite 
cause. 
The most striking peculiarity connected 
with sexual reproduction, next to its almost 
universal occurrence, lies in its remarkably 
complex character. Moreover, its effects on 
the development of the vegetable kingdom 
have been extremely far-reaching, and have 
profoundly influenced the direction of evolu- 
tionary progress, as interpreted by a study 
of the life-history of the plants themselves. 
The sexual act itself stands in strong 
antithesis to vegetative propagation, for it 
does not directly involve an increase, but a 
reduction in the number of cells. Two cells, 
