THE JUNGERMANNIA GROUP 



287 



the stem, and a third row of small modified leaves on the lower 

 surface (Fig. 254, B}. The stems of mosses, on the contrary, are 

 almost always upright, and the leaves are arranged radially, so 

 that the stem has no upper 

 or lower surface. 



The antheridia of the 

 leafy liverworts are borne 

 singly along the stem at 

 the bases of the lateral 

 leaves (Fig. 255, B) on cer- 

 tain branches which are 

 frequently much smaller 

 than the vegetative shoots 

 (Fig. 255, A). The arche- 

 gonia are developed in clus- 

 ters at the ends of branches. 



The sporophyte (Fig. 

 256, A) has a stalk which 

 elongates rapidly just be- 

 fore the spores are ready to 

 be shed, so that the spore 

 case is raised above the 

 gametophyte (Fig. 254, C), 

 as in the mosses. How- 

 ever, the spore case is much 

 less complex than that of 

 the mosses, being a simple 

 capsule that splits length- 

 wise into four parts at maturity (Fig. 254, D). There are spirally 

 thickened filaments, or elaters (Fig. 256, C), among the spores, 

 as in Marchantia, and these structures are not found in the 

 mosses. The foot of the sporophyte (Fig. 256, A) is always well 

 developed in the leafy liverworts.* 



* To THE INSTRUCTOR : Good material of the leafy liverworts frequently 

 furnishes better subjects for type study of the liverworts than Marchantia. 



FIG. 256. The sporophyte of a leafy 

 liverwort (Porella) 



, section of a sporophyte still contained with- 

 in the parent archegonium, whose neck n is 

 shown above, the foot deeply sunken in the 

 tissue of the gametophyte : a, archegonia of 

 the terminal group, which were not ferti- 

 lized ; I, leaf-like envelopes. B, the four-lobed 

 spore mother cell, which develops four spores 

 (tetrad). C, an elater 



