128 CHAP. XVI. PHOTOSYNTHESIS WITHOUT CARBON DIOXIDE 



Effect of Increasing Strengths of Solution 

 of Malic Acid 



Preliminary experiments enabled me to find the range 

 within which increased supply of the acid enhanced the rate 

 of photosynthesis, avoiding an excessive dose which proves 

 to be as toxic as an excessive supply of carbon dioxide. 

 The following is an account of a typical experiment on the 

 effect of supplying increasing strengths of malic acid. The 

 particular specimen of Hydrilla evolved oxygen at a rate of 

 56 c.mm. per hour in distilled water ; in a solution of malic acid 

 4»i parts in 10,000 the activity was enhanced to 290 c.mm. 

 per hour ; double the strength of this dose, i.e. 8-2 parts in 

 10,000, increased it to 460 c.mm. per hour ; 12-3 parts in 

 10,000 enhanced the rate of evolution of oxygen still further 

 to 510 c.mm. per hour. This was the climax, for a stronger 

 solution of 16-4 parts in 10,000 produced a depression, the 

 rate being reduced to 455 c.mm. per hour ; the results are 

 given in the following tabular form. 



Table XVII.- — Photosynthesis with Increasing Strengths 

 of Malic Acid Solution 



I reproduce (fig. 36) the photosynthetic curves of two 

 different specimens of acid Hydrilla, the one under increas- 

 ing C0 2 -concentrations, and the other under increasing 

 strengths of malic acid. The two curves show a remark- 

 able resemblance throughout the entire range of reaction. 

 The reversal took place just above 9 mg. of C0 2 in the 

 one and 12-3 parts of malic acid in 10,000 in the other. 



