CHAPTER XVII 



EFFECT OF VARIATION OF TEMPERATURE ON 

 PHOTOSYNTHESIS 



Determination of the respiratory loss — Importance of accurate adjust- 

 ment of temperature — Shock-effect caused by sudden variation — 

 Determination of thermometric minimum for photosynthesis — 

 Phenomenon of accommodation — Thermometric minimum for auto- 

 nomous pulsation — Determination of the optimum point for photosyn- 

 thesis — Effect of intensity of light and of season — Photosynthetic 

 curve under variation of temperature — Optimum point for various 

 activities of plants — Determination of the temperature-coefficient 

 of photosynthesis by the differential method. 



The investigation of the effect of variation of temperature 

 on photosynthesis involves the determination (i) of the 

 thermometric minimum, (2) of the optimum, and (3) of the 

 general character of the photosynthetic curve. 



In order to avoid errors of observation, special precau- 

 tions have to be taken to produce and maintain constancy 

 of the different temperatures, and an estimation must be 

 made of the loss of oxygen in respiration. The volumes 

 of oxygen evolved at different temperatures are, of course, 

 reduced to standard temperature and pressure. 



Loss of Oxygen in Respiration 



Determination of oxygen by the C0 2 respired. — Ten 

 different plants of standard size were put into a bottle 

 filled with 100 c.c. of oxygenated distilled water, another 

 similar bottle filled with distilled water serving as a con- 

 trol. They were kept in the dark for 12 hours at a definite 

 temperature. After the expiration of this period the water 

 in both the bottles was tested separately by the volumetric 

 method (standard alkali and phenolphthalein). The con- 



