5 8 MORPHOLOGY 



ual Batrachospermum, and once believed to be an independent plant 

 it was named Chantransia. These chantransia forms multiply by spores 

 (not tetraspores) ; but sooner or later one of the lateral branches 

 develops as the sexual Batrachospermum filament. The chantransia 

 form, therefore, is only one phase in the life history of Batrachospermum, 

 giving rise to sexual branches of very different kind, which once were 

 thought to be independent plants. It should be noted that both these 

 phases constitute one vegetative body, the product of the carpospore. 

 This striking variation in form, where one structure gives rise directly 

 to a very different structure, is found in the life history of many plants, 

 and it has been referred to in connection with the life history of Charales. 



Polysiphonia. This form is selected to illustrate the more complex 

 and the more numerous red algae. This more complex majority in- 

 cludes in the life history the formation of the characteristic tetraspores, 

 which are non-motile, naked, asexual spores, a group of four being pro- 

 duced by each one-celled sporangium. In the maturing sporangium 

 there are two successive nuclear divisions, and in connection with these 

 four nuclei the spores are organized. This definiteness in the number 

 of nuclear divisions indicates some definite process, which will be con- 

 sidered later. The sporangia of red algae occur in various situations, 

 either at the tips of short lateral branches or embedded in the thallus, 

 in the latter case being either scattered or in special receptacles. 



Polysiphonia has received its name because the complex branching 

 filament is polysiphonous (figs. 149-151), consisting of a central row 

 of elongated cells (axial siphon), surrounded by peripheral cells (cor- 

 tical cells). Ordinarily there are three kinds of individuals: (i) male 

 plants, bearing antheridia; (2) female plants, bearing procarps; and 

 (3) sexless plants, bearing sporangia that produce tetraspores. 



Male plant. The antheridia occur in clusters on special branches 

 (fig. 149). The structure of an antheridial branch is as follows: From 

 the cells of the axial siphon large numbers of small cells arise laterally, 

 each of which gives rise in turn to a terminal cell. An oblique division 

 of this terminal cell cuts off a cell which is the antheridium (fig. 152). 

 The antheridium does not discharge its protoplast as a sperm, as in 

 Nemalion, but is cast off bodily, in this case the so-called " spermatium " 

 being an antheridium that functions directly as a sperm. Its nucleus 

 does not divide, as in Nemalion, so that the antheridium contains only 

 one male nucleus. A second or even a third antheridium may be cut 

 off successively by the same parent cell. 



