SECT. I CRYPTOGAMS 429 



known. Morphological comparison points rather to a connection between the 

 Bryophyta and the Brown Algae, the nmltilocular ganietangia of which (in some 

 genera already difl'erentiated into oogonia and antheridia) may be regarded as 

 homologous structures leading to the archegonia and antheridia of the Arche- 

 goniatae. Thus the antlieridium of the lower Liverworts (Ricceaceae, Marclian- 

 tiaceae) shows a cellular construction in agreement with that of the gametangia of 

 Brown Algae (c/. Figs. 366, 367, and Figs. 293, 295) ; it is distinguished by the 

 possession of a sterile, protective layer of cells forming the wall, and tlie ditferentia- 

 tiou of this can be regarded as an adaptation to a terrestrial mode of existence. 

 Further, among the Brown Algae, in Dictyota. there is an alternation of generations 

 agreeing with that of Bryophyta, though the gametophyte and sjiorophyte are 

 similar in tlieir vegetative structure. The tetrasporangia of the s])orophyte of 

 Dictyota correspond to tlie spore-mother-cells of the sporophyte of the Bryophyte ; 

 their endogenous position in the latter may be related to the influence of a terrestrial 

 mode of life. While the form of the gametophyte in the thalloid Liverworts shows 

 many points in common with the thallus of certain Brown Algae, tlie sporophyte 

 of the Bryophyta proceeds early to the development of its sjiores, and ceases 

 growth witliout a division into vegetative organs. It tlius becomes essentially 

 different from the gameto[ihyte with which it is by origin homologous ('°^). 



The two very distinct classes of Bryopbytes may be briefly charac- 

 terised as follows : — 



1. Hepaticae (Liverworts). — The sexual generation, with poorly 

 developed and generally not distinctly difl'erentiated protonema, is 

 either a dichotomously divided thallus or is developed as a leafy and, 

 with few exceptions, dorsiventral shoot. In the majority of Hepaticae, 

 in addition to spores, the capsule j^roduces also elaters, sterile cells 

 which, in their typical development, become greatly elongated and 

 provided with spiral thickenings (Fig. 372, F). They conduct 

 nourishment to the developing sporogenous cells, and at maturity, 

 •after the opening of the capsule, serve to separate and scatter the 

 sjDores. Only in one order, Anthocerotaceae, does the capsule have a 

 columella, or an axial mass of sterile cells, which also conduct the 

 metabolic products to the developing spores. 



2. Musci (Mosses), — The protonema of the sexual generation is 

 usually well developed and distinctly defined, and the moss plant is 

 always segmented into stem and leaves. The leaves are arranged 

 spirally in polysymmetrical, less frequently in bisymmetrical, rows. 

 The capsule is always without elaters, ])ut, excej^t in one genus, it 

 always possesses a columella. 



Class I 



Hepaticae (Liverworts) (^- ") 



The Hepaticae are divided, according to the structure of the 

 sporogonium and the segmentation exhibited by the sexual generation, 

 into four orders : the llkciaceae, Marchantiaceae, and Anthocerotaceae, 



