LIFE HISTORY OF A LIVERWORT 



211 



In the first two and last of these orders the plant body is a 

 thallus, either closely resembling the prothallus of the 

 ferns, or freely branching. In the third order the plant 



FIG. 154. A leafy liverwort (Porella navicularis). Male plant, about 

 natural size. (After M. A. Howe.) 



body is leafy (foliose), and in this respect somewhat re- 

 sembles certain true mosses, for which it is often mis- 

 taken (Figs. 1 54 and 155). In the first two and last orders 

 the thallus always shows dorso- ventral differentiation. 



