Variations in Quantity of Leaf Pigments. 45 



dichromate solution and of the yellow pigments as corresponding to 

 one another in colour intensity. 



Potassium dichromate 

 Carotin. solution, 



0-0286 grams per litre. 2 grams per litre. 



100 mm 101 mm. 



50 mm 41 mm. 



25 mm 19 mm. 



Potassium dichromate 

 Xanthophyll. solution, 



0-0284 grams per litre. 2 grams per litre. 



100 mm 72 mm. 



50 mm. 27 mm. 



25 mm 14 mm. 



ii. Results. 

 1, The Total Content of Green and Yellow Pigments. 



As far as his observations go, Willstatter finds the chlorophyll 

 content of leaves varies from 0-6% to 1"2% of the total dry weight, 

 the greater number of leaves contain about 0-8% of chlorophyll of 

 which three-quarters is chlorophyll a and one quarter chlorophyll 

 b. Much bigger variations were observed between leaves from the 

 same plant than between the mean contents of leaves from different 

 plants. Shade leaves were found to be much richer in chlorophyll 

 than sun leaves in proportion to the dry weight, but not in propor- 

 tion to the leaf surface ; for shade leaves, as is well known, are 

 often very thin. 



The total content of the yellow pigments (xanthophyll and 

 carotin) was found to vary in different leaves from 0-1% to 0-2% of 

 the dry weight, the xanthophyll contributing from 007% to 0'12%, 

 the carotin from 0-03 to 0-08%. 



Shade leaves were not found to contain a higher percentage of 

 yellow pigments corresponding to their higher content of chlorophyll. 



Leaves collected at different hours of the day were examined ; 

 the time of day was found to be without influence on the 

 chlorophyll content or the ratio of the pigments. As this is of 

 importance in regard to the function of the pigments in the 

 processes of carbon assimilation we may quote here two tables 

 taken from Willstatter's book to show how slight this variation is. 



