BRYOPHYTES 



93 



I. HEPATIC AE 



General character. — The liverworts are of great interest on account of 

 their apparent relationship to the green algae on the one hand, and to the 

 higher plants on the other. Through them the aerial habit of green plants 

 seems to have been established. This change in habit involved more 

 compact and better protected bodies, and the change from swimming 

 spores to aerial spores; but it is important to note that the swimming 

 habit was retained by the sperms. Three groups of liverworts are recog- 

 nized, each having developed special features: (i) Marchantiales, 

 (2) Jungermanniales, and (3) Anthocerotales. 



(i) Marchantiales 

 This group may be represented by its two prominent families, Riccia- 

 ceae and Marchantiaceae; the former representing the more primitive 

 forms, the latter the highly specialized forms. 



Ricciaceae. — The genus Riccia (including Ricciocarpus) contains 

 aquatic as well as terrestrial species, so that this family belongs to both 

 the water and the land. 



Gametophyte. — The gametophyte is a flat, dorsiventral body and 

 branches dichotomously (fig. 202). This dorsiventral habit results in a 



differentiation of the body into two 

 distinct regions. The dorsal (upper) 



Fig. 202. — Riccia: showing 

 the dorsiventral, dichotomously 

 branching gametophyte, which 

 puts out rhizoids and scales from 

 its ventral surface; the rows of 

 dark bodies in the bottom of the 

 conspicuous grooves on the dorsal 

 surface are sporophytes, which 

 show also the position formerly 

 occupied by the archegonia. 



Fig. 203. — Riccia: section through dorsal 

 region of thallus, showing the intercellular clefts, 

 often enlarging into chambers, by means 

 of which the cells containing chloroplasts are 

 bathed by an internal atmosphere. — After 

 Barnes and Land. 



region is composed of green tissue, the intercellular spaces developing 

 as numerous deep and narrow clefts, which in some cases broaden 

 into chambers (fig. 203), so that all the green cells are bathed by 



