200 



PRACTICAL BOTANY 



185. Vaucheria: reproduction. As suggested in Sect. 183, 

 it sometimes occurs tliat brandies are left as separated in- 

 dividuals by the death 

 of the older portions 

 of the plant. This re- 

 sults in vegetative re- 

 production. Asexual 

 reproduction may be 

 started by having the 

 end of a branch cut off 

 by a cross wall. The 

 part that is thus cut 

 off proceeds to form 

 an immense zoospore 

 (Fig. 162, ^, 5). The 

 wall which contains it 

 breaks, and it slowly 

 emerges, and, after a 

 period of separate ex- 

 istence in the water, it germinates and forms a new plant 

 (Fig. 162, C). This zoospore is composed of many cells. It 

 is therefore a com- 

 pound zoospore, and 

 iscoenocytic. But the 

 compound zoospore 

 produces only one 

 new plant. Forma- 

 tion of zoospores may 

 be induced in the lab- 

 oratory by keeping 

 Vaucheria plants in a 

 dish of shallow water. 

 Another kind of re- 

 production may occur 

 at the same time that zoospores are being formed, though it 

 usually occurs at other times. Upon the sides of the plant 



Fig. 162. The formation of zoospores by 

 Vaucheria 



A, a piece of a plant at the tip of which a section 

 has' been cut oft to prod iice the zoospore (2) ; B, 

 a zoospore which has become free from the plant 

 which formed it, and has assumed the rounded 

 swimming form; C, a zoospore germinating to 

 form a new plant. Considerably magnified 



Fig. 163. The sexual reprodnotive structures 

 of Vaucheria (V. sessilis) 



0, oogonia ; A, antheridia. Note the opening in the 

 antheridium for exit of sperms, and in the oogonia 

 for their entrance to the large eggs. Greatly enlarged 



