POLYSIPHONIA 327 



on the end of a branch and at first apparently consists of two 

 cells, a basal one called carpogonium and a much elongated 

 terminal one called trichogyne. The two ceUs are not separated 

 by a wall and the nucleus soon disappears from the trichogyne 

 and the two cells then appear as a single one with a bulbous base 

 and a hair-like extension. The carpogonium corresponds to the 

 oogonium in other Algae, for it contains a protoplast which func- 

 tions as an egg. 



The antheria, which are borne in clusters at the ends of short 

 branches, are single cells, and the protoplast of each antheridium 

 becomes binucleate and functions as a sperm. After these 

 binucleate protoplasts are discharged from the antheridia, they 

 depend upon water currents to carry them to the female sex 

 organs as they have no cilia. When they come in contact with 

 the trichogyne, the two walls in contact are resorbed, and the two 

 male nuclei of the sperm pass into the trichogyne through the 

 perforation. A number of sperms may discharge their nuclei 

 into the same trichogyne, but only one male nucleus passes on 

 into the carpogonium and fuses with the female nucleus. After 

 fertilization, the carpogonium develops numerous short filaments, 

 each of which bears a spore, called a carpospore, at its tip. The 

 carpospores, short filaments, and the carpogonium together con- 

 stitute the structure known as a cystocarp. The carpospores 

 upon germination develop sexual plants, thus completing the life 

 history. 



Polysiphonia. — This plant (Fig. 283) is a representative of 

 the complex forms of Red Algae. It is a much-branched complex 

 filament and is so named because it has a central row of elongated 

 cells (axial siphon), enclosed by peripheral cells. This plant 

 presents much differentiation and ordinarily a hfe history in- 

 volves three types of individuals — male, female, and sexless 



plants. 



The male plants bear their antheridia on very short lateral 

 branches which arise from the axial siphon and bear the an- 

 theridia somewhat laterally on their tips. The protoplast of an 

 antheridium contains only one nucleus and is not discharged as 

 in Nemalion, but the antheridium breaks off bodily and is floated 

 to the trichogyne. 



The female plant produces a procarp more complex than that 

 of Nemalion. The procarp consists of other cells in addition to 



