Ch. X] 



CONFERVOID ALG^ 



423 



plants, but in others upon different ones, 

 in which case we may speak of male and 

 female plants. Furthermore, in some 

 species the male plants, here very small, 

 actually develop upon the oogonia of the 

 female plants (Fig. 292), and release their 

 sperm cells in close contiguity to the open- 

 ings into the egg cells. 



A more elaborate development of the 

 plant body is found in the gracefully 

 branched Chcetophoracece. The culmination 

 of the reproductive mechanism occurs in 

 Coleochcete, a group of small disk-shaped 

 forms which grow attached to water 

 plants (Fig. 293). Reproduction occurs 

 through zoospores, but also sexually with 

 formation of an oospore as in (Edogonium. 

 Two interesting new features, however, 

 appear. First, an enveloping case of cells 

 develops around the oospore from the 

 subjacent tissue, — an arrangement which 

 becomes frequent in higher Algae. Second, 

 the oospore, a resting spore, produces not 

 a new plant directly, but a structure of 

 several cells, each of which gives rise to a 

 zoospore; and these grow to new plants. 

 Thus we have a new structural stage 

 introduced between fertilization and the 

 formation of new plants, an arrangement 

 anticipated in Ulothrix, and itself antici- 

 patory of the regular alternation of gen- 

 erations in higher plants. For this and 

 other reasons, some authorities hold that 

 Coleochcete stands very close to the ances- 

 tral Algae from which the first land plants 

 were evolved. 



Fig. 292. — (Edo- 

 gonium, sexual re- 

 production ; x 300. 



Above, (E. nodulo- 

 sum ; portion of a 

 filament showing a 

 ripe oogonium, with 

 opening entered by 

 the sperm cell ; below 

 the oogonium are 

 the small antheridial 

 cells, from each of 

 which escape two 

 sperm cells, shown 

 just to the right. 

 Above is a zoospore. 

 (After Bergen and 

 Davis.) 



Below, (E. cilia- 

 turn; an oogonium, 

 with attached male 

 plant, from the an- 

 thcridiinn of which ■ 

 sperm cell has passed 

 into the egg coll. 

 (After Pringsheim.) 



