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. IS4.-A leafy liverwort {Porella navicularis) . Male plant, about 

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



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

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

 taken (Figs. 154 and 155). In the first two and last orders 

 the thallus always shows dorso-ventral differentiation. 



