THE GREAT GROUPS OF BRYOPHYTES 



317 



radial^ in contrast with the dorsiventral thallus, referring 

 to the fact that it is exposed to similar conditions all 

 around, and its organs are arranged about a central axis 

 like the parts of a radiate animal. This position is much 

 more favorable for the 

 chlorophyll work than 

 the dorsiventral posi- 

 tion, as the special 

 chlorophyll organs 

 (leaves) can be spread 

 out to the light freely 

 in all directions. 



The leafy branch 

 of the Mosses usually 

 becomes independent 

 of the thallus by put- 

 ting out rhizoids at its 

 base (Fig. 290), the 

 thallus part dying. 

 Sometimes, however, 

 the filamentous proto- 

 nema is very persist- 

 ent, and gives rise to a 

 perennial succession of 

 leafy branches. 



At the summit of 

 the leafy gametophore, 

 either upon the main 

 axis or upon a lateral 

 branch, the antheridia and archegonia are borne (Fig. 277). 

 Often the leaves at the summit become modified in form 

 and arranged to form a rosette, in the center of which 

 are the sex organs. This rosette is often called the " moss 

 fiower," but it holds no relation to the flower of Seed- 

 plants, and the phrase should not be used. A rosette may 

 contain but one kind of sex organ (Fig. 277), or it may 



Fig. 290. A moss (Bryu7?i), showing base of a 

 leafy branch (gametophore) attached to the 

 protonema, and having sent out rhizoids. On 

 the protonemal fihiment to the right and be- 

 low is the young bud of another leafy branch, 



— MULLER. 



