ALGAE 73 
As a rule, the fresh-water Rhodophycez are simpler 
in structure than their marine relatives, and proba- 
bly represent a more primitive type of structure from 
which the others have been derived. It is not impos- 
sible that these simple fresh-water forms may also be 
intermediate between the green alge and the higher 
Rhodophycee. It must be admitted, however, that, with 
the exception of the Bangiacex, a group whose affinity 
with the true Rhodophycee has been questioned, all the 
fresh-water forms, although simpler in structure, are 
typical Rhodophycez, so far as the reproductive parts 
are concerned. 
The motile zodspores of the brown and green alge 
are replaced in most Rhodophycee by the so-called 
tetraspores, formed four together in a common mother- 
cell, much as zodspores are formed. These escape from 
the mother-cell and form new plants at once (Fig. 19, 
A, B). 
The sexual reproduction shows certain peculiarities 
which are not found elsewhere in the vegetable king- 
dom, although there are certain analogies in the fertil- 
ization of some fungi. The antheridium (Fig. 20, C) 
is made up of a great number of small cells which arise, 
as short branches, very much crowded together. The 
contents of the terminal cells escape in the form of a 
naked, but non-motile cell, or spermatium, which differs 
in structure from the spermatozoids of other alge, 
mainly in the absence of cilia. So far as is known, the 
conveyance of the sperm-cell to the female reproductive 
organ, or procarp, is dependent upon the movements of 
the water. 
The female reproductive organ of the Rhodophycee 
