98 MANUAL OP BOTANY 



CHAPTEB IV. 



Group II. 

 BJRYOPHYTA. 



The plants of this group show a great advance in complexity 

 of structure when compared with the Thallophyta. There is a 

 well-marked antithetical alternation of generations, the gameto- 

 phyte giving rise to the sporophyte uniformly as the result of 

 the fertilisation of a female sexual cell. The spore on germina- 

 ting always produces a gametophyte. 



The gametophyte is the body which is usually termed the 

 plant, the sporophyte is a stalked spherical or ovoid structure 

 which arises upon it and never has a separate existence. The 

 gametophyte shows considerable morphological differentiation ; 

 in the lower forms it is a thallus ; in some a little higher it is a 

 thalloid stem bearing a few rudimentary leaves ; in the highest 

 forms it is a leafy shoot. There are never any true roots, but 

 a number of unicellular root-hairs, or multicellular filaments, 

 attach it to the soil. It always contains chlorophyll, the 

 arrangement of the plastids presenting considerable variety. 



The gametophyte consists of two parts. When the spore 

 germinates it does not at once produce what we recognise as 

 the plant, but gives rise to a structure called the protonema 

 {fig. 858), which is sometimes a flattened plate-like body and 

 sometimes a much-branched filament. Upon this protonema 

 the plant arises usually as a lateral bud, which grows up into the 

 form of the adult gametophyte. 



The protonema contains chloroplastids in all its cells ; it 

 exists usually for a short time only, though in some of the 

 Mosses it persists for a long period. Generally in the Hepaticse 

 the protonema gives rise to only one plant ; in the Mosses, on the 

 other hand, several may spring from it. 



The anatomical differentiation of the gametophyte is not 

 very great. The tissue is nearly all parenchymatous, but in 

 some of the Mosses there is in the axis an indication of vascular 



