THALLOPHYTA: ALGAE 



91 



A C 



Fig. 77. Polysiphonia. ^, portion of plant bearing tetraspores, X 160; B, portion of male 

 plant bearing clusters of antheridia, X200; C, portion of female plant with cystocarp con- 

 taining carpospores; also a single carpospore, X80. 



spores are formed in groups of four in a one-celled sporangium (Fig. 77 A). 

 They are called tetras'pores. Chromosome reduction occurs in connection 

 with the formation of the tetraspores, and so each is haploid. Upon 

 germination, two tetraspores from each 

 sporangium produce male plants and two 

 produce female plants. These sexual plants 

 are like the tetrasporic ones in general 

 appearance. 



The antheridia occur in dense clusters on 

 special lateral branches of the male plants 

 (Fig. 775). In their formation, a number 

 of cells arise laterally from the cells of the 

 axial filament, giving rise to a simple mono- 

 siphonous branch. Each cell of this branch 

 develops two-celled lateral branches. An 

 oblique division of the terminal cell of each 

 branch produces a unicellular antheridium 

 (Fig. 78). The antheridium discharges its 

 protoplast, which functions as a nonmotile 

 male cell, or spermatium. Other antheridia 

 may then be budded off the same terminal 

 cell. 



Besides the carpogonium and trichogyne, 

 the procarp includes several other cells as 

 well. It arises from a large 'pericentral cell 

 that first produces a row of four cells, the terminal one becoming the 



Fig. 78. Diagram of antheridial 

 branch of Polyalphonia, showing 

 three stages in the development 

 of an antheridium (o), whose 

 protoplast functions as a male 

 cell. {After Yamanouchi.) 



