THALLOPHYTES 33 
sporophyte. In fact, in this case, the doubling of chromosomes in the 
formation of the oospore is followed immediately by their reduction 
during the divisions of the oospore. 
Conclusions. Upon considering the assemblage of green algae here 
brought together under Confervales, the following general statements 
may be made : The body is a simple filament, a branching filament, or 
a flat thallus, and is either completely septate or partially coenocytic. 
Zoospores are produced abundantly, and are generally biciliate, Oedo- 
gonium being a notable exception. The sexual reproduction ranges 
from isogamy to a stage of heterogamy in which distinct oogonia and 
antheridia are developed. The zygospores may give rise directly to 
new plants or may produce zoospores ; but the oospores always develop 
zoospores, a process which culminates in Coleochaete in a specially or- 
ganized zoospore-producing body. 
(d) Siphonales 
General character. This is a very well-defined group, comprising 
mostly marine forms. The distinguishing character, suggested by the 
name, is that the plant body has no cross walls, being one continuous 
multinucleate protoplast enclosed by the peripheral wall, a kind of body 
called coenocytic. In this case the body is completely coenocytic, as 
distinguished from such partially coenocytic bodies as those of Clado- 
phora and Sphaeroplea. The bodies are more or less diffusely branch- 
ing, and in some of the marine forms the differentiation of the body is 
remarkable, as in Bryopsis, Caulerpa, Acetabularia, etc. The two 
prominent fresh-water forms are as follows. 
Botrydium. This interesting plant develops in damp places, such 
as the mud of drying-up ponds, wet plowed ground, boggy fields, and 
especially on flood plains. It appears as groups of little green, balloon- 
shaped bladders, about the size of a pin's head, which grip the substratum 
by means of colorless, rhizoidal branches (fig. 90). Numerous small 
nuclei are embedded in the thin wall layer of cytoplasm, and in the 
aerial part there are numerous chloroplasts. 
The asexual methods of reproduction are various, dependent upon 
varying conditions. A new bladder may bud out from the aerial part, 
send rhizoidal branches into the substratum, and then become separated 
from the parent by a wall. If covered with water, the whole inflated 
aerial portion may be converted into a sporangium producing a multi- 
tude of uniciliate zoospores (figs. 91, 92) These zoospores germinate 
