THE EVOLUTION OF THE PLANT BODT 



31 



cellular body, the bulk of whose cells are protected from dessica- 

 tion by a special epidermal covering. The important contact 

 with the earth, source of the life-sustaining water and minerals, is 

 secured by numerous hair-like rhizoids which serve the double 

 purpose of anchorage and absorption. Being prostrate in habit, 

 Marchantia and all liverworts have no supporting tissue. Division 

 of labor among the cells results in greater inter-dependence 

 among the cells of the thallus than is found in any of the preced- 



FiG. 11. — Liverworts are a group of simple land plants living in the shaded 

 and moist habitats of wooded ravines. 



ing types. The cells with chloroplasts are found immediately 

 beneath the epidermal layer; below this photosynthetic tissue 

 (fig. 1 2) is a layer of storage cells, larger in size and with fewer 

 chloroplasts. On the undersurface of the epidermis develop the 

 rhizoids which lack chloroplasts and act as absorptive cells. 

 Throughout the body there exist numerous connecting air spaces 

 which permit free passage of water and gases from one cell to 

 another. The daily life of the liverwort is only slightly different 

 from that of its aquatic relatives. The water arrives at the photo- 

 synthetic cells by diffusion from the lower cells of the thallus, 



