SUMMARY 221 



the evolution of oxygen corresponding to the production 

 of an amount of carbohydrate as small as the millionth 

 of a gramme. 



The value 0-8906 of the oxygen-carbohydrate factor 

 in normal specimens undergoes a definite variation accord- 

 ing to the previous conditions, plants from a sun-exposed 

 pond exhibiting a higher value, those from semi-darkness 

 a lower. 



