CH. X] CONFERVOID ALG^B 421 



bright green growths on the stones of sluggish streams, 

 ponds, troughs, and fountains. The plant body is a fila- 

 ment, 2 or 3 centimeters long, attached by a colorless basal 

 cell; the other cells, all alike, contain each an encircling 

 chloroplastid. Asexual reproduction is effected through 

 zoospores, which are small and four-ciliate, and formed sev- 

 eral together in any cell. After swimming about for a time 

 they come to rest and produce new filaments. Some cells 

 produce gametes, which look much like the zoospores but are 

 smaller and two-ciliate; they conjugate in pairs, and the 

 resultant resting zygospores germinate to several zoospores 

 which grow to new filaments. This formation of zoospores 

 instead of a new plant directly, an arrangement already de- 

 scribed in Chlamydomonas (page 417), has apparently the ad- 

 vantage of developing several plants from one act of fertili- 

 zation, and anticipates an analogous method prevalent in 

 higher plants. Certain species of Ulothrix produce not only 

 zoospores and gametes, but also intermediate bodies which 



FIG. 290. Cladophora species ; X f. (From Oltmanns, Morphologic 

 und Biologie der Algen.) 



can germinate to new filaments either with or without conju- 

 gation ; and this fact supplies a certain confirmation of a con- 

 clusion probable upon other grounds, that gametes originated 

 from zoospores in which the first fusion was accidental. 



