272 THE BIOLOGY OF THE PLANT 



"Zoospore"? Stain with iodine, and look for 

 nuclei. Treat a moving zoogonidium with two 

 per cent, salt solution to plasmolyze it. Do you 

 find a cell- wall apparent ? Treat in like manner 

 a zoogonidium which has come to rest, and com- 

 pare it with the first. 



Try to find filaments in which the formation of 

 zoogonidia is going on, and study the process. Is 

 the zoogonidium formed by the union of sexual 

 cells ? Is the protoplasm of the zoogonidium sep- 

 arated from that of the cavity of the filament ? 

 Where a mature zoogonidium is found, watch to 

 see it escape from the filament. 



Study a zoogonidium which has come to rest, in 

 order to see the process of germination. 



General Questions. — As regards structure, is Vaucheria 

 more or less complicated than 8j)irogyra% As regards 

 reproduction, which is the more complicated ? "What is 

 the advantage in having zoogonidia ? 



What means of dispersal has Vaucheria ? Of protec- 

 tion ? 



Draw a filament, showing the stages in the formation 

 of a zoogonidium, a mature zoogonidium, and the ger- 

 mination of the same. 



