GAMETOGENESIS AND SPOROGENESIS 



197 



mary nucleus of the antheridium initiates a series of mitoses giving rise 

 to a large number of nuclei. About each of these is organized a laterally 

 biciliate spermatozoid. In the oogonium the primary nucleus initiates 

 a series of three mitoses, the protoplasm then subdividing to form eight 

 large eggs. In related genera only four, two, or one egg may be produced, 

 the remaining nuclei degenerating. ^ In Vaucheria, which is coenocytic, 

 many colorless, elongated spermatozoids with two cilia near one end are 

 organized about the nuclei in the antheridium. In the maturing oogo- 



l''^'a" 



Fig. 114. — Gametogenesis and syngamy in Vaucheria sessilis. A-C, differentiation of 

 spermatozoids in coenocytic antheridium. D, early stage in development of oogonium. 

 E, mature egg with one nucleus and many plastids. F, gametic nuclei uniting in egg c, 

 chloroplast; n, nucleus; r, receptive papilla; s, spermatozoids. {After Oltmanns, 1895.) 



nium all but one of the many nuclei retreat to the main thread in a mass 

 of " Wanderplasm " or degenerate, that one remaining as the nucleus of 

 the single large egg^ (Fig. 114), In Polysiphonia, non-motile male 

 gametes, or spermatia, are budded off successively from the antheridial 

 cell, each of them being supplied with a nucleus formed by a division of 

 the antheridial nucleus. The female nucleus lies in the enlarged base 

 of the carpogonium, a cell which elongates to form a receptive trichogyne 

 above. 



The most characteristic spores in algae are the zoospores, which swim 

 about actively by means of cilia. Except for their larger size they 

 resemble the male gametes of their respective genera, being terminally 



^ For recent accounts, see Tahara (1927, 1929). 



3 Oltmanns (1895), Heidinger (1908), and Couch (19326) report retreat; B. M. 

 Davis (1904), M. Williams (1926), and Mundie (1929) report degeneration. 



