REPRODUCTION 



267 



to reproduce itself by zoospores or by gametes. Observa- 

 tion shows that the same cell never reproduces itself by both 

 means. External influences must, therefore, swing the 

 balance in one direction or the other. 



The following is a table showing the results of Klebs's 

 experiments on Hydrodictyon : . 



HYDRODICTYON UTEICULATUM 



ZOCSPOEES GAMETES 



Light absolutely necessary to zoo- 

 spore formation, strong light most 

 favorable. 



Light not absolutely necessary. 



Darkness checks zoospore forma- Darkness favors gamete over zoo- 

 tion. spore formation. 



Transfer from darkness to light 

 stimulates. 



Flowing water retards or pre- 

 vents zoospore formation, still 

 water stimulates, considerable 

 volume needed. 



Inorganic nutrient salts very 

 strongly induce zoospores to form. 

 Zoospores especially abundant 

 when transfer in the light from nu- 

 trient solution to water. 



Cane sugar not stimulating. 



Maltose very stimulating in light. 



Transfer from light to darkness 

 stimulates. 



Small volume of still water stimu- 

 lates gametes to form. 



Inorganic nutrient 

 gamete formation. 



salts retard 



32° maximum temperature for 

 zoospores. 



8° too low temperature for zoo- 

 spores. 



Only floating nets form zoospores. 



Canesugarin 0.5^10% stimulates. 



Maltose and cane sugar stimulate 

 in darkness. 



Cells with slight tendency to zoo- 

 spore formation produce zoospores 

 in lighted, gametes in darkened 

 maltose solution. 



33°-34° maximum temperature for 

 gametes. 



Same for gametes. 



Slightly higher temperature will 

 retard zoospore and stimulate ga- 

 mete formation. 



Nets grown on filter paper wet 

 with water, or better, with cane 

 sugar solution, form gametes. 



