Vegetal Evolution. 151 



their leaves and stems. As the water is absorbed by 

 the roots, it thus traverses their whole system. 



Plants, like animals, also breathe or respire, for 

 oxygen is essential to their existence. Respiration 

 involves the riddance of superfluous carbon, which is 

 accomplished by the carbon combining with the 

 oxygen of the air, after which it is exhaled as car- 

 bonic acid. 



(b) Reproduction. — Cryptogams practically repro- 

 duce similarly to flowering plants. The fructification 

 is necessarily more insignificant, but the mechanical 

 operation differs only in details. Some cryptogams, 

 like phanerogams, are hermaphrodite, that is, they 

 generate buds or spores which of themselves repro- 

 duce the parent plant. Others are monoecious, that 

 is, male and female organs grow on the same plant ; 

 while others are dioecious, that is, male and female 

 organs grow on separate plants. All cryptogams 

 exhibit two modes of reproduction : — (a) Asexual 

 (without distinct sexual organs of reproduction); (J?) 

 sexual (with distinct sexual organs of reproduction). 



" Alternation of generations " also occurs in plants. 

 Thus spores are emitted which on maturing do not 

 reproduce the parent plant, but a different form. 

 This, on germinating, may either evolve a spore re- 

 producing the parent type, or the metamorphosis may 

 continue through several more generations before 

 completing the cycle. Many cryptogams reproduce 

 both asexually and sexually, as well as by cuttings 

 and shoots. Indeed, the only requisite for vegetal 



