THALLOPHYTES 
57 
at the end of a branch; the carpogonium, a cell which is the equivalent of 
the oogonium of other algae in that it contains the female nucleus, al- 
though no definite egg is organized ; and the trichogyne, an elongated, 
hairlike cell terminating the carpogonium, which acts as the receptive 
cell with which the sperms come in contact (fig. 147). At first the trich- 
ogyne contains its own nucleus, but soon this nucleus disappears, and 
the two cells appear as a single one, with a bulbous base and a hairlike 
extension. 
In fertilization the floating sperm comes in contact with the tricho- 
gyne, the two walls in contact become resorbed, and through the per- 
foration one or both of the male nuclei are discharged. More than one 
sperm may come in contact with the trichogyne, and several male nuclei 
may be discharged into it ; but only one passes on into the carpogonium 
and fuses with the female nucleus (fig. 147). 
Cystocarp. As a result of this act of fertilization, numerous short 
filaments are developed by the carpogonium, and at the tip of each one 
a spore is formed (rounded off), called the carpospore (fig. 148). This 
whole structure carpospores, filaments, and central carpogonium 
is the cystocarp, but it is not a cystocarp representative of this organ 
among the red algae, as will be seen in the other illustrations. The 
carpospores upon germination give rise to the sexual plants, thus com- 
pleting the life history. 
In such a life history, the sexual plants may be multiplied directly 
by tetraspores (when they occur) ; but the sexual act results in the for- 
mation of a cystocarp, a structure producing carpospores, which in turn 
reproduce the sexual plants. 
Batrachospermum. This fresh-water form is related to Nemalion, 
and will serve to illustrate other features of the simpler red algae. The 
life history is very much like that of Nemalion; but, in some cases, 
while the carpospores are forming, loose filaments appear as outgrowths 
from cells at the base of the carpogonium, representing the case of the 
true cystocarp of other groups, the envelope or case having suggested the 
name. This encasing outgrowth from adjacent sterile cells is a very 
common accompaniment of the act of fertilization, not only among the 
red algae, but also in other groups. It will be remembered that a sim- 
ilar envelope is developed by Coleochaete and by the Charales, but in 
the latter case it appears before fertilization. 
Germination. When the carpospore of Batrachospermum germinates, 
it gives rise to a filamentous body very different from that of the sex- 
