igo TRANSACTIONS OF ROYAL SCOTTISH AKl;ORlCULrURAL SOCIKTY. 



This is probably due to the difference in the anatomical structure 

 of the leaves of the broad-leaf and coniferous species. The 

 extremely small size of the cells of the leaf parenchyma in broad- 

 leaf species means the presence of a large amount of living 

 protoplasm and chloroplasts, and consequently a larger amount 

 of living, acting substance within the same space. 



On the basis of these experiments, Lubimenko claims to have 

 established the following facts in regard to the photochemical 

 work of different forest trees : 



(i) The photochemical work of the green leaf is determined 

 by its anatomical structure and the inherent qualities of its 

 chloroplasts. 



(2) The influence of the anatomical structure of the leaf is 

 felt mainly in light of medium intensity; the influence of the 

 inherent qualities of the chloroplasts, on the other hand, is 

 strongly apparent in light of low and high intensities. 



(3) Chloroplasts of different species are sensitive to light in 

 different degrees ; chloroplasts of shade-enduring species are 

 more sensitive than chloroplasts of light-needing species. 



(4) Species with more sensitive chloroplasts begin to 

 decompose carbon dioxide and reach a maximum of assimilative 

 photochemical energy in light of much lower intensity than 

 species with less sensitive chloroplasts. 



(5) The curve of the photochemical work of a green leaf has 

 a distinct optimum, which is reached in different species under 

 different intensities of light and is determined by the inherent 

 qualities of the chloroplasts. 



(6) It is very probable that the difference in sensitiveness of 

 chloroplasts of different species is due to a difference in the 

 absorptive capacity of the chlorophyll. 



(7) The conception of "light-loving" and "shade-enduring" 

 trees has a real foundation as far as the process of assimilation 

 of carbon is concerned. Leaves of shade-enduring species are 

 able to replace the carbon dioxide expended in the mere process 

 of respiration in much weaker light than are leaves of light- 

 loving species. The optimum of assimilation in tolerant species 

 lies within the limits of normal sunlight, while the optimum of 

 assimilation in light-needing species lies beyond those limits. 



These conclusions are also corroborated by Grafe's experi- 

 ments carried on at the Institute of Plant Physiology, at Vienna 

 (VViesner, 1907), though for another purpose. Green leaves 



