272 



LEAFY LIVERWORTS 



rather drier situations than do the simple thalloid forms ; the 

 leaves, unlike those of Mosses, are usually lobed (Fig. 147, A), and 

 sometimes even deeply divided. Some of the commonest of 

 the foliose Liverworts belong to the genera Lophocolea and 

 Cephalozia, whose structure is typical of these forms. Here 

 there is a prostrate stem, bearing on either flank a row of over- 

 lapping, sessile, 

 two-lobed leaves 

 (Fig. 147, A) and, 

 on the underside, 

 a few small scales 

 with tufts of 

 rhizoids arising 

 from their base. 

 The two lobes of 

 the leaves are 

 often folded to- 

 gether. In some 

 of the foliose 

 forms the leaves 

 are complicated 

 by the modifica- 

 tion of the lower 

 lobe into a water- 

 receptacle. Frul- 

 lania, a common 

 epiphyte on tree- 

 trunks, affords 

 an extreme ex- 

 ample, in which 

 this lobe is de- 

 veloped as a 

 small, helmet-shaped pitcher (Fig. 148). In the leafy Liverworts 

 the growing point of the stem is invariably a single cell. 



The thallus of most Liverworts exhibits little anatomical 

 differentiation. In such an one as Pellia, for example, all the 

 cells, apart from their elongated form in the region of the midrib, 

 are similar in shape, and most of them contain the numerous 

 small discoid chloroplasts which are typical of Bryophyta 



FIG. 148. Photomicrograph of a small portion of the 

 epiphytic Liverwort Frullania tamariscini, show- 

 ing the pitcher-like lower lobes of the leaves. 

 [Photo, E. J. S.] 



