THALLOPHYTES 
45 
been derived from the Chlorophyceae, and it has possibly developed 
independently from such organisms as gave rise to the green algae. 
None of the true brown algae are one-celled, the simplest being a simple 
conferva-like filament, and the group also includes forms with very com- 
plex bodies. Sexual reproduction is probably present in all the forms, 
having been discovered recently in Laminaria, and is chiefly repre- 
sented by isogamy, but a small group has attained heterogamy. 
The two orders of brown algae are distinguished by their methods of 
reproduction : Phaeosporales, characterized by the formation of zoo- 
spores and by prevailing isogamy; Fucales, characterized by the absence 
of zoospores and by well-developed heterogamy. 
(a) Phaeosporales 
General character. This group includes the large majority of brown 
algae and also the most bulky. The zoospores and gametes are alike, 
and are produced in special 
organs the sporangium 
and the gametangium. It 
will not be possible or profit- 
able to give an account of the 
numerous families, but the 
general features of the group 
may be indicated by the 
following illustrations: 
Ectocarpus. This form 
occurs as tufts of branching, 
many-celled filaments. The 
filament consists of a single 
row of cells, the body being 
called monosiphonous. If 
the body consists of several 
parallel rows of cells, as in 
certain other brown algae, 
it is 
FIGS. 120-122. Ectocarpus: 120, monosipho- 
alled polysiphonOUS. nous filament bearing a sporangiurr on a short 
Sporangium The SPO- ^ atera ^ branch; i 21, a zoospore, showing the laterally 
biciliate character (after KUCKUCK); 122, filament 
rangmmisasmglecell, which bearing a gametangium rpluri iocular sporangium"), 
in some forms is a cell of 
the filament changed in function and usually in size; and in other 
forms is developed at the end of a special short lateral branch (fig. 120). 
