134 



PHOTOS YNTHESIS 



man's theory of limiting factors. She found that increasing the tem- 

 perature produces an increase in the rate of photosynthesis only up to 

 a certain point. Here some other factor, either light intensity or carbon 

 dioxide-concentration determines the rate and a further increase in tem- 

 perature has very little effect on photosynthesis. However, when there 



-w 



10* 



20* 



SO* 



40* 



50* 



Fig. 12. — Influence of temperature on the rate of photosynthesis. 



(From Matthaei.) 



is an excess of light and carbon dioxide, it is ai)parent that the rate of 

 photosynthesis increases rapidly with increasing temperature and it is con- 

 cluded that "corresponding to each temperature there is a certain definite 

 amount of assimilation which may be termed 'maximal assimilation' for 

 that temperature. This cannot be exceeded and will not be reached unless 

 both light and carbon dioxide supply are adequate." 



Most of the older work on the influence of temperature on photo- 



