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, 



