454 General Botany 



(3) Sexual reproduction. A sexual spore, or oospore, is 

 formed by the union of two gametes. The gametes may be 

 similar in size and appearance, as in Ulothrix, or they may be 

 unlike, as in (Edogonium, where one gamete accumulates a large 

 food supply and the other is small and motile. In either case, 

 the one gamete corresponds to the sperm and the other to the 

 egg that is found in higher plants. The union is the process 

 of fertilization. The oospore may germinate immediately, 

 but more often it remains dormant for a period of weeks or 

 months. 



Other genera of green algae. The most beautiful of the 

 larger green algae are the Draparnaldias, having a main filament 

 with little plumose tufts of lateral branches. Closely related 

 are the Stigeocloniums. Both are frequently found in springs 

 and small temporary streams. 



Among the most readily recognized forms are the species of 

 Spirogyra, with their spiral chloroplasts — sometimes as many 

 as sixteen bands in each cell ; and Zygnema, with cells marked by 

 two large, radially branched chloroplasts. 



Vaucheria is a common group found in pools, ditches, and 

 streams and on moist soil. These algae are remarkable in having 

 no cross-walls in the long and much-branched vegetative fila- 

 ments. In the warmer seas are a number of genera related to 

 Vaucheria, that attain considerable size. 



Species of Cladophora are highly branched. They are coarse 

 forms, found attached to rocks in lakes and swift-flowing streams 

 everywhere. 



Plankton algae. The microscopic plants and animals that 

 Qoat or swim in all bodies of water make up what is known as the 

 plankton (Greek : planktos, wandering). It includes hundreds of 

 species of algae, that multiply rapidly and go through their life 

 cycles in a few days. These algae are so minute that they can 

 be collected only by passing the water through silk bolting cloth, 

 or filter paper. Nevertheless, they are quite as important as 



