12 



THE SYNTHESIS OF CARBOHYDRATES 



Lundegardh agrees with Harder that the factors of light in- 

 tensity and carbon dioxide concentration, when above the 

 normal pressure of the natural atmosphere, mutually influence 

 one another. A like difference between sun and shade leaves 

 has been observed by Stalfelt * in the gymnosperms Picea 

 excelsa and Pinus sylvestris ; he found that the intensity of 

 photosynthesis was greater in shade leaves than in sun leaves 

 at the same light intensity as is shown by the following table 

 in which the light intensity is in percentages of open daylight 

 and the photosynthesis is in mgs. of carbon dioxide assimilated 

 per hour per gram of fresh weight. 



The difference in the behaviour of sun and shade leaves pre- 

 sumably is due to the fact that the ground shade flora is, from 

 the character of its habitat, surrounded by an atmosphere 

 richer in carbon dioxide than the upper air and the air of more 

 open situations ; also shade leaves are characterized by a more 

 delicate structure, wherefore impediments to a rapid inter- 

 change between the internal atmosphere of the leaf and that 

 of the surrounding air are to a greater or lesser extent removed. 

 This structural factor is of importance, possibly of great 

 importance, in the carbon assimilation of the higher plants, 

 wherefore comparisons of the photosynthetic ability of the 

 leaves of different plants or of the same plant grown in 



* Stalfelt : " Mcdd. Stat. Skogsforsoksanst," 1921, 21, 221. 



