io4 



MORPHOLOGY 



apical cell with two cutting faces, and (3) the stage of the apical cell 

 with three cutting faces. It should be noted that this is one more stage 

 than shown by Aneura (see p. 102), but it is not absolutely certain that 

 the second stage occurs, at least with any regularity. The apical cell 

 of the last stage, cutting off three series of segments, gives rise to three 

 rows of leaves — two dorsal and one ventral. The mature dorsiventral 



body consi >t s of a distinct branch- 

 ing axis (stem) bearing two rows 

 of dorsal leaves (figs. 233-235), 

 which are usually two lobed ; 

 and one ventral row of very 

 small leaves against the sub- 

 stratum (amphigastria), variable 

 in form (fig. 233). The two 

 lobes of the dorsal, chlorophyll- 

 bearing leaves are equal or un- 

 equal; and in certain epiphytic 

 forms the lower (ventral) lobe 

 forms a small sac containing 

 water. 



The kinds of vegetative multi- 

 plication are the same as given 

 under Anacrogynae (see p. 102), 

 but the gemmae are usually 



tria) in the middle line, and the dorsaf leaves simpler, often consisting of only 



Figs. 233-235. — Porella: 233, ventral 

 view, showing two ventral leaves (amphigas- 



with their ventral lobes; 234, portion of ga- 

 metophyte showing three antheridial branches; 

 235, gametophyte with two archegonial 

 branches bearing terminal sporophytes (open- 

 ing by four valves), and three other arche- 

 gonial branches. 



one or two cells separating from 

 the leaf margins. 



Sex organs. — The antheridia 

 of Porella are on short lateral 

 branches, which differ very 

 much in appearance from the sterile branches (fig. 234). They are 

 conspicuous on account of the closely imbricated leaves, in each of 

 whose axils there is a single, long-stalked, and globular antheridium 

 (fig. 236). The development of the antheridium is as described under 

 Anacrogynae (see p. 102). 



The archegonia also occur on short lateral branches (fig. 235), being 

 found in a group at the apex. This group is usually surrounded by a 

 rosette of modified (usually enlarged) leaves. The archegonia arise 

 from segments of the apical cell, and finally the apical cell itself becomes 



