300 PLANT STUDIES 
sperm, the organs producing the two being known as oogo- 
nium and antheridium respectively. 
(5) AlgcB the main line. The Algae, aquatic in habit, 
appear to be the Thallophytes which lead to the Bryophytes 
and higher groups, the Fungi being regarded as their de- 
generate descendants ; and among the Algae the Chloro- 
phyceae seem to be most probable ancestors of higher forms. 
It should be remembered that among these Green Algae the 
ciliated swimming spore (zoospore) is the characteristic 
asexual spore, and the sexual spore (zygote or oospore) is 
the resting stage of the plant, to carry it over from one 
growing season to the next. 
196. General characters of Bryophytes. The name given 
to the group means "moss plants," and the Mosses maybe 
regarded as the most representative forms. Associated 
with them in the group, however, are the Liverworts, and 
these two groups are plainly distinguished from the Thallo- 
phytes below, and from the Pteridophytes above. Starting 
with the structures that the Algae have worked out, the 
Bryophytes modify them still further, and make their own 
contributions to the evolution of the plant kingdom, so 
that Bryophytes become much more complex than Thallo- 
phytes. 
197. Alternation of generations. Probably the most im- 
portant fact connected with the Bryophytes is the distinct 
alternation of generations which they exhibit. So impor- 
tant is this fact in connection with the development of the 
plant kingdom that its general nature must be clearly under- 
stood. Probably the clearest definition may be obtained by 
tracing in bare outline the life history of an ordinary moss. 
Beginning with the asexual spore, which is not ciliated, 
as there is no water in which it can swim, we may imagine 
that it has been carried by the wind to some spot suitable 
for its germination. It develops a branching filamentous 
growth which resembles some of the Conferva forms among 
the Green Algae (Fig. 275). It is prostrate, and is a regu- 
