THALLOPHYTES 



57 



at the end of a branch; the car polonium, 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 caqwgonium, 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 Ncmalion, 

 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- 



