176 



STRUCTUKAL BOTANY 



duct of its assimilation is deposited in the form of a fatty 

 oil. 



2. KEPKODUCTION 



Vaucheria produces reproductive cells of two kinds 

 asexual and sexual. The asexual reproduction affords a 

 rapid means of propagation, and goes on chiefly when the 

 plant is growing in abundance of water, and generally 

 under conditions that suit it. 



The protoplasm accumu- 

 lates and becomes denser 

 at the end of a branch, 

 which assumes a club-like 

 form. The enlarged end 

 is then separated from the 

 rest of the filament by a 

 transverse septum, for 

 Vaucheria forms cell-walls 

 in connection with its repro- 

 ductive organs, though not 

 elsewhere, except in case 

 of injury. The cell thus 

 formed may be called the 

 zoosporangium. The entire contents of the zoosporangium 

 constitute a single zoospore of relatively large size, clothed 

 over its whole surface with numerous short cilia (see 

 Fig. 74). 



The sporangium opens at the apex ; the expulsion of 

 the zoospore is helped by the expansion of mucilage 

 contained in the cell, but depends to a great extent on 

 its own movements. The opening is much narrower 

 than the zoospore, which has to push its way through, 

 and to change its form in the process (see Fig. 75, A). 



FIG. 74. Zoospore of Vaucheria 

 sessilis. To the left is shown the 

 end of a filament, just cut off, by 

 the wall (w), to form a zoospor- 

 angium. Magnified 25. To the 

 right is a zoospore covered with 

 the numerous cilia (c). Magnified 

 95. (After Strasburger. ) 



