424 



BOTANY 



PART II 



usually in pairs, at the ends of the radiating branches. Each antheridium 

 consists of a single thin -walled cell, in which the whole of the protoplasm 

 is consumed in the formation of one uninucleate SPERMATITJM ; in Batracho- 

 spermum and Nemalion the nucleus of the spermatium divides into two. The 

 spermatia are nearly spherical, and are invested with a thin outer membrane 

 or cell wall. They are non-motile, unlike the ciliated spermatozoids of the 

 other Algae, and have therefore received a distinctive name. In consequence of 

 their incapacity for independent movement, they must be carried passively by the 

 water to the female organs, which are sjtuated near the antheridia at the ends 

 of other branches. The female organ is called a CARPOGONIUM (Fig. 367), 

 and consists of an elongated cell with a basal flask-shaped portion prolonged 

 into a filament, termed the TRICHOGYNE. The basal portion contains the 

 nucleus of the egg and the chromatophores, while the trichogyne functions 



FIG. 365.Callithamnioncorymbosum. A, Closed 

 sporangium; B, empty sporangium with 

 four extruded tetraspores. (After THURET. ) 



FIG. 366. Batrachospermum monili- 

 forme. Branches bearing antheridia. 

 At s*, a free spermatium ; at s, 

 another just escaping ; at v, an 

 empty antheridium. (x 540. After 

 STRASBURGER.) 



as a receptive organ for the spermatia, one or two of which fuse with it, 

 and the contents, escaping through the spermatium wall, pass into the carpo- 

 gonium. The sperm nucleus passes down the trichogyue and fuses with the 

 nucleus of the egg-cell. The fertilised egg, which becomes limited from the 

 trichogyne by a wall, does not become converted directly into an oospore, but, 

 as a result of fertilisation, numerous branching sporogenous filaments (GOXIMO- 

 BLASTS) grow out from the sides of the ventral portion of the carpogonium. At the 

 same time, by the development of outgrowths from cells at the base of the carpo- 

 gonium an envelope is formed about the sporogenous filaments. The whole 

 product of fertilisation, including the surrounding envelope, constitutes the 

 fructification, and is termed a CYSTOCARP. The profusely-branched sporogenous 

 filaments become swollen at the tips and give rise to spherical, uninucleate spores 

 known as CARPOSPORES, which are eventually set free from the envelope. In 

 the case of Batrachospermum the carpospores produce a filamentous protonema, 

 the terminal cells of which give rise to asexual unicellular spores. These spores 

 serve only for the multiplication of the protonema. Ultimately, however, one 

 of the lateral branches of the protonema develops into the sexually differentiated 

 filamentous thallus. The production of spores by the protonema is analogous to 

 the formation of tetraspores by other Florideae. 



The homologies underlying the variously-constructed sexual organs of the Red 



