BRYOPHYTA 



205 



dolabrate apical cell, as in all the Musci. The archegonia have a long 

 stalk, a massive venter, and a long twisted neck. The number of neck 

 canal cells is greater than in any other group of plants. The sporophyte 

 displays the greatest amount of sterilization of potentially sporogenous 

 tissue seen in the Bryophyta. The sporogenous tissue arises from the 

 outer part of the endothecium and has the form of a hollow cylinder. 

 The seta is elongated, no pseudopodium being formed. The capsule 

 shows an extraordinary degree of specialization, both in the organization 

 of an operculum, peristome, and apophysis, and in its internal differentia- 

 tion of tissues. It contains both green tissue and stomata. 



COMPARISON OF LIVERWORTS AND MOSSES 



The most important distinguishing characters of the Hepaticae (liver- 

 worts) and Musci (mosses) are as follows: 



Hepaticae 

 Gametophyte almost invariably dorsiven- 



tral; thalloid or leafy 

 Leaves, where present, without a midrib 



Rhizoids unicellular and mostly 

 unbranched 



Protonema, where present, small and tran- 

 sitory 



Sporophyte remaining enclosed by the 

 calyptra, or breaking through only 

 when spores are ripe 



Elaters usually present 



Musci 

 Gametophyte typically radial ; leafy 



Leaves generally with a midrib (except in 



Sphagnum and Andreaea) 

 Rhizoids septate, mostly branched 



Protonema usually conspicuous, rela- 

 tively persistent 



Sporophyte breaking through the calyp- 

 tra at an early stage of development 

 (except in Sphagnum) 



Elaters absent 



GENERAL CONCLUSIONS 



The bryophytes, undoubtedly derived from aquatic ancestors, are the 

 simplest group of green plants growing on land. Their position in the 

 plant kingdom is an expression of the degree of evolutionary progress they 

 have made, but is not necessarily an indication of their phylogenetic rela- 

 tionship to the higher plants. One theory holds that the bryophytes are 

 an ancient stock from which the pteridophytes have been derived. 

 Another theory contends that the pteridophytes have originated directly 

 and independently from the algae and that, therefore, the bryophytes 

 represent a blindly ending line of descent. But even if the latter view 

 should prove to be the correct one, the first land plants may have passed 

 through a general stage of development similar to that reached by the 

 bryophytes of the present. 



The bryophytes differ from the algae in the possession of archegonia, 

 multicellular antheridia, and an established heteromorphic alternation of 

 generations. Because the liverworts are simpler than the mosses, it 

 seems very probable that they are more primitive and thus more ancient 



