316 



THALLOPHYTES 



toplasts of the other fihiment as shown in Figure 271. The 

 protoplasts are unhke, for one migrates while the other does 

 not. In behavior the migrating protoplasts may be regarded 

 as sperms and the passive ones as eggs, although they show no 

 differentiation in size or structure. Also, the filament which 

 loses its protoplasts may be regarded as male and the receiving 

 filament as a female individual. The zygospore builds about 

 itself a heavy wall and at the end of a rest period develops 

 directly into a new filament. 



It is now seen that the Conjugales stand quite apart from the 

 previous groups in having no zoospores or swimming gametes. 



Fig. 272. — A species of Vaucheria {Vaucheria sessilis), showing the 

 coenocytic habit of the filament, the oogonia at o, the antheridia at a, and the 

 sperms escaping from an antheridium and entering an oogonium at s. X 75. 

 Partly drawn from nature and partly diagrammatic. 



and in having a peculiar kind of conjugation, in which entire 

 protoplasts fuse and commonly reach each other through tubes. 

 Although the gametes are alike in size and structure, they show 

 some differentiation in the way they behave. The group is 

 considered a highly specialized one. 



Tubular Algae (Siphonales). — These Algae, of which there are 

 about 300 species, are so named because the plant body, no matter 

 how long and thread-like, has no cross walls and, therefore, 

 resembles a tube filled with protoplasm. The protoplasm con- 

 tains many nuclei and many chloroplasts, and may be regarded 

 as a much elongated multinucleate cell or as a filament with cross 

 walls omitted. Such a plant body is called a coenocyte. The 

 majority of the Siphonales are marine forms, living in warm seas, 



