REPRODUCTION IN PLANTS 113 



selves have suffered reduction and lost their motility, can 

 reach the egg and perform the act of fertilization. Frequently 

 this sexual differentiation extends to the flower as a whole, 

 since some flowers bear only stamens and others only carpels 

 and are known as male and as female flowers respectively. 

 Moreover, male and female flowers may be borne on separate 

 plants, in which case the plants themselves are called male 

 and female. In brief, the terminology which rightly is appli- 

 cable only to the sexual generation is, for convenience, trans- 

 ferred to the asexual generation, in consequence of the fact 

 that vicarious sexual functions are reflected back to it through 

 the almost complete suppression of the actual sexual genera- 

 tion itself. 



If we glance back over the reproductive processes in plants, 

 we are impressed with the fact that reproduction is, to a 

 very large extent, asexual. The great masses of thallus 

 vegetation, represented by Seaweeds and their allies, in- 

 crease in bulk chiefly by vegetative cell division, and new 

 individuals are formed in profusion by fragmentation and 

 spore formation. In the Mosses, where the sexual generation 

 is prominent, beds of moss are developed chiefly by the 

 asexual budding of the sexual plant, while spore formation 

 holds a prominent place in the increase and dissemination of 

 individuals. In the Ferns and Flowering Plants, which are 

 to all intents and purposes asexual plants, since the sexual 

 phase is relegated to an increasingly obscure position in the 

 life history, reproduction is not only by spores, but also by 

 cuttings, bulbs, fragments of leaves, etc. In brief, reproduc- 

 tion, unaccompanied by sexual phenomena, is apparently 

 amply sufficient for the propagation of plants. 



However, it will be noted that sexuality has persisted from 

 its simple origin when spores of unicellular plants performed 

 the sexual act and became gametes. The gametophyte 



