io6 
MORPHOLOGY 
evolution. It is this gradual disappearance that must be noted in 
connection with subsequent groups. 
(3) ANTHOCEROTALES 
General character. This is a small group comprising four genera: 
Anthoceros and Notothylas of the temperate regions ; Dendroceros, an 
epiphytic tropical genus; and Megaceros, a genus recently described from 
Java. Although few in numbers, the group is of great morphological in- 
terest on account of the claims made for it that it possibly represents the 
ancestral forms of pteridophytes. Its possible relation to the mosses 
also further emphasizes its important genetic position. It differs so 
much from the other liverworts as to have suggested its separation from 
them as a third great group of bryophytes, coordinate with liverworts 
and mosses. In Marchantiales and Jungermanniales there is extensive 
differentiation of the body of the gametophyte, either in structure or in 
form; but in Anthocerotales there is a simple gametophyte, while the 
sporophyte is the most complex among liverworts. 
Gametophyte. The body of the gametophyte is a simple thallus (figs. 
239, 240), almost as simple as that of Aneura, and much simpler than 
that of Marchanlia. The margin is often wavy, lobed, or crisped ; and 
in Dendroceros the lobing in 
some cases suggests rudi- 
mentary leaves. The thallus 
matures by means of an 
apical cell with four cutting 
faces, the preceding stages 
appearing as usual. There 
are two marked peculiarities 
of the gametophyte body in 
most of the genera : (i) the 
usually single large chloro- 
plast, generally in contact 
with or even more or less 
investing the nucleus; and 
(2) the mucilage cavities, 
which open by clefts on the 
ventral surface. In these cavities endophytic Nostoc colonies occur. 
The sex organs are developed on the dorsal side of the thallus, but iii 
certain features they differ strikingly from those of other bryophytes. 
FIG. 237. Anthoceros: an antheridial chamber 
containing three antheridia. 
