266 



PRACTICAL BOTANY 



LIVERWORTS 



248. Riccia. Among the bryophytes the liverworts are sim- 

 pler than the mosses, and some of the liverworts are extremely 

 simple. Upon moist soil at the margins of ponds and streams 

 and sometimes free-floating in quiet water, the small, green, 

 disk-like Riccia or Ricciocarpus plants may be seen (Fig. 222). 

 Upon careful observation, root-like projections (rhizoids) may 

 be observed upon the lower surface. The plant is two-lobed, 

 with a depression or notch between the 

 lobes. This body is frequently spoken 

 of as a thallus, though it is not like the 

 thallophyte body. The rhizoids extend 

 downward and backward from the notch. 

 The upper surface of Riccia is greener 

 than the lower surface. Near its margin 

 the plant may be but one or a few layers 

 of cells in thickness. Evidently Riccia, 

 though a prostrate plant, is much more 

 complex than any of the algae. It is more 

 complex in that it has distinct upper and 

 lower surfaces, with root-like hairs grow- 

 ing from the lower surface. It is also to 

 be noted that it has a distinct apical or 

 growing end and a basal end. Chlorophyll 

 is borne in the compact body cells, and 

 living as the plant does, upon damp earth or in water, it can 

 readily secure the materials from which foods are manufactured 

 It is more complex than the protonema of moss, but less so 

 than the leafy shoot. 



In reproducing itself each individual plant of Riccia forms 

 within its tissues both kinds of reproductive organs. One of 

 these is an archegonium, the tip of which just reaches the 

 upper surface of the plant. In the swollen part of the arche- 

 gonium is the large egg cell, which is therefore deeply em- 

 bedded in the plant tissues. The antheridia also open to the 



FIG. 222. A simple liver- 

 wort (Ricciocarpus) 



It has distinct upper and 

 lower surfaces, bears rhi- 

 zoids (r) on the under 

 surface, and branches 

 from a midrib into leaf- 

 like structures (I) . About 

 five times natural size 



