REPRODUCTION 



265 



ZOOSPORES 



3-8 are constant stimulus to 

 zoospore formation. 



26 ' is maximum temperature for 

 zoospore formation but not for 

 growth. No acclimation to this. 



10~-20 r are indifferent tempera- 

 tures, exercising neither stimulating 

 nor depressing effects in passing 

 up or down. 



Raising temperature from indiffer- 

 ent to high, or lowering from in- 

 different to low, exercises no stimu- 

 lus; but raising from 3 to 15 

 stimulates. 



Culture in inorganic nutrient solu- 

 tion favors nutrition and growth, 

 but not zoospore formation. Trans- 

 fer from such to less nutritious acts 

 as stimulus to zoospore formation. 



Sugars and other nutritious or- 

 ganic compounds do not stimulate 

 to formation of zoospores. 



More oxygen required than for 

 growth. 



Flowing water, by favoring nutri- 

 tion and growth, retards or pre- 

 vents zoospore formation. Con- 

 versely, transfer to still water acts 

 as a stimulus. Accommodation to 

 still water followed by rapid growth 

 and cessation of zoospore forma- 

 tion. 



From this table certain influences stand out as especially 

 efficient stimuli to the formation of reproductive bodies. 

 Thus light, which furnishes the energy for the manufacture 

 of the materials needed to form the sexual organs and ele- 

 ments, must fall upon the plant in intensity, not only 

 sufficient for this, but also great enough to act as a distinct 

 stimulus to use the manufactured substance in this special 

 way. Light furnishes the energy for one kind of work ; more 

 energy of this same kind sets and keeps other processes in 

 operation. Food, when available in abundance, thus reliev- 

 ing the plant of the necessity of diligently manufacturing 



SEXUAL ORGANS 



Sex-organs form, but develop more 

 slowly than at higher temperatures. 

 Same for sex-organs. 



Same for sex-organs. 



Same for sex-organs. 



Same for sex-organs. 



Favor formation and develop- 

 ment of sex-organs. 



More oxygen required than for 

 zoospore formation. 



No fertile plants in running water. 

 Become fertile in still water. 



