2l6 CHAP. XXIV. CARBOHYDRATE-FORMATION 



It will be noted that an evolution of i • 10 c.c. or 



i ioo c.mm. of oxygen accompanied an increase of weight of 



1-30 mg. The evolution of 1 c.mm. of oxygen thus corre- 



1 * ^o 



sponded to the formation of — = 1-2 X io~ 6 erm 



1000 X 1100 ° 



of carbohydrate. I have already explained how, by adjusting 



the capacity of the Bubbler, it is possible to record the 



evolution of even 0-2 c.mm. of oxygen. The Bubbling 



Apparatus can thus be made so sensitive as to record the 



photosynthetic production of carbohydrate smaller than a 



millionth of a gramme. 



Constant Value of Oxygen-Carbohydrate 

 Factor in Normal Specimens 



It has been shown that in normal specimens, grown in 

 the pond exposed to the northern light of the sky, there 

 is a definite relation between increase of weight of the 

 plant and the weight of oxygen given out by it under the 

 action of light, such that the increase of weight due to the 

 production of carbohydrate may be found by multiplying 

 the weight of oxygen produced by o • 8906. How extremely 

 close is the actual increase of weight to the calculated value 

 will be seen from the detailed results given of five other 

 experiments carried out with specimens from the same 

 pond, but on different days and under light of various 

 intensity. In the following table, the first column gives 

 the number of the specimen, the second column the duration 

 of the experiment, the third column the volume of oxygen 

 produced at temperature t° C. and pressure p in mm. of 

 mercury. The fourth column gives the volume of oxygen 

 at N.T.P. ; the fifth the weight of the oxygen ; the sixth 

 the weight of carbohydrate obtained on multiplying the 

 weight of oxygen by the oxygen-carbohydrate factor o • 8906. 

 In the seventh column is given the actual increase of weight 

 obtained by weighing. 



