114 



EVOLUTION OF PLANTS 



phases, the protonema and gametophore. The spore 

 on germination produces a filamentous, or occasionally 

 flat, alga-like growth, the protonema (Fig. 29, A, B, C, 



jor), and upon this 

 arise special buds or 

 branches which grow 

 into leafy stems, the 

 gametophores (Fig. 29, 

 A, B, C, &), which bear 

 the sexual organs. The 

 leaves of the gameto- 

 phoric branches are 

 commonly arranged 

 spirally, and the 

 branches seldom are 

 flattened as in the 

 foliose Hepaticse. 

 While there are cer- 

 tain superficial resem- 

 blances between the 

 leafy stems of the 

 mosses and foliose 

 liverworts, there are 

 differences which make 

 it extremely improb- 

 able that the former have been derived from the latter. 

 The two forms are rather to be considered as parallel 

 developments. In the Musci the structure of both leaves 

 and stem is as a rule much more complex than in the 

 Hepaticse, and there is usually present a central strand 

 of conducting tissue, quite wanting in both stem and 

 leaf in the latter group. 



FIG. 29 (Musci or True Mosses). A, the 

 liverwort-like protonema of a peat- 

 moss (Sphagnum) with the leafy shoot, 

 k, buckling out from it ; B, the fila- 

 mentous protonema, pr, of a common 

 moss (Funaria), with a very young 

 leafy bud, k ; C, an older stage of the 

 same moss; D, the full-grown leafy 

 gametophore, g, with the sporophyte, 

 sp, still connected with it ; ar, the re- 

 mains of the archegonium carried up 

 by the growth of the sporophyte. 



