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 
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 (Bryuiri), 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. 
