Vegetal Evolution. 153 



external conjugation. Two cells on adjoining tiers 

 or stalks of cells bulge out their cell walls, meet, 

 coalesce, and form a connecting tube. One cell, 

 probably the female, drains the contents of the other, 

 the male cell ; the former then enlarges, bursts, and 

 discharges numerous spores which germinate into new 

 plants. 



The usual sexual mode of reproduction is effected 

 by means of sexual receptacles, the male containing 

 motile bodies, spermatozoids (as in the protophyta), 

 which on emission, propel themselves in the water and 

 fasten on the female receptacles, which they pierce 

 and fertilise with their protoplasm. Ultimately the 

 female receptacles rupture and emit spores, or zoo- 

 spores, generally provided with vibratile cilia, by the 

 aid of which they move about until they eventually 

 settle down and grow according to their type. 



The chief point to remember about reproduction — 

 and it is the same in all the kingdoms — is that it is 

 automatic. No plant intentionally forms a definite 

 number of seeds, any more than it constructs a 

 definite number of leaves or flowers. A plant can 

 thus no more help reproducing itself than it can 

 help growing, provided its natural conditions 

 prevail. 



Fertilization is thus a combined mechanical and 

 chemical process, and consists, firstly, in the proto- 

 plasm of the pollen cell — the male — penetrating to 

 the protoplasm in the embryo sac of the female ; 

 both substances then coalesce, grow by chemical 



