366 



BOTANY OF THE LIVING PLANT 



clearly two-lobed, and the lobes are often unequal (Fig. 310, A). Some- 

 times a lobe may become highly specialised, as in Frullania (Fig. 3 10, B], 

 where that which is downward-directed develops as a water-sac, or 

 pitcher, effective in collecting and holding water in this epiphytic or 

 rock-dwelling genus. On the other hand, in Trichocolea the leaves 

 may be divided into narrow laciniae, which collectively hold water 

 as in a sponge. Thus it appears that there is a wide scale of adaptation 



FIG. 310. 



A, Scapania nemorosa, dorsal view of the leafy shoot, which bears a sporogonium 

 at its tip. B, Frullania tamarisci, view of leafy shoot from below, to show the 

 ventraf row of leaves, and the two lateral rows, of which the lower lobes form 

 pitchers. A has the " succubous," B the " incubous " disposition of the 

 leaves. (After Cavers.) 



of the gametophyte in Liverworts. Its results offer analogies with 

 the special adaptations seen in the sporophyte of Flowering Plants. 



The sexual organs are essentially similar to those of the Mosses ; 

 but there are differences in their segmentation. This suggests that 

 their origin may have been distinct. In the thalloid Liverworts they are 

 always borne on the morphologically upper surface ; but by various 

 means they are carefully protected, being sometimes sunk deeply in 

 the thallus (Fig. 311). In the Jungermanniae they are covered in by 

 envelopes, the number and variety of which give useful features in 

 classification. A particular interest attaches to those which develop 

 a " marsupium," that is a nursing-sac surrounding the archegonia, 



