THE GREAT GROUPS OF BEYOPHYTES 



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 

 flower," 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 (Bnjvrn), showing base of a 

 leafy branch (gametophore) attached to the 

 protonema, and having sent out rhizoids. On 

 the protonemal filament to the right and be- 

 low is the young bud of another leafy branch. 

 — Muller. 



