42 OUTLINES OF PLANT LIFE. 



In each phase, a body of form and structure suited to its 

 special work is produced. In the higher liverworts and 

 mosses both phases have nutritive work to do, but in many 

 this is confined to the gametophyte, and in all the gameto- 

 phyte carries on the greater part of it. To this phase, there- 

 fore, attention is first given. 



Liverworts. 



51. The thallus. — The form and structure of the vegeta- 

 tive body of the simplest liverworts is scarcely different from 

 that of some of the green algae. The body is a thallus with 

 rhizoids (fig. 37). The rhizoids are usually filaments arising 



Fig. 37.—^, plants of Ficcia sorocar^a, on the ground. Gametophyte phase. Nat- 

 ural size. B, a vertical section of one of the thick lobes of the thallus, showing nearly 

 uniform structure. The thallus has nearly covered^ over two young sporophytes 

 which appear as thougli in the interior. Rhizoids arise from the ventral side and 

 flanks. Magnified about 25 diam.— After Bischoff. 



from the under side and flanks of the thallus. They serve to 

 fasten the thallus to the substratum, and perhaps assist it in 

 absorbing water. The thallus is usually thin and flat, though 

 sometimes much crisped. Most liverworts lie broadside to 

 the substratum. Very rarely is the thallus erect and attached 

 by a narrow stalk. 



52. The dorsiventral thallus. — In the simplest forms the 

 thallus is uniform in structure from upper to under side. In 

 others there is a decided difference between the two sides. 

 The upper part is green, while the under is not. In one 

 family there are large air-chambers in the upper part of the 



