452 



Prof. C. Timiriazeff. 



[Apr. 30, 



chlorophyll. It has since been proposed to denote this part of the 

 process by the special name of chlorovaporisation. My old friend the 

 late Professor Deherain pointed out a highly interesting fact, subse- 

 quently confirmed by Professor Sorauer and especially by M. Jumelle, 

 that these two principal functions of the leaf the assimilation and 

 the chlorovaporisation are in a certain sense complementary, the 

 evaporation falling off in the presence of carbon dioxide. This result 

 would seem quite natural, since the same source of energy must be 



100 



o-i 



02 



0-3 0-4 



FIG. 10. 

 0-5 0-6 



07 0-8 0-9 



90 



80 



6o 



a 







ssii tilatior 



Asaii ailatk 



,+Chlor ^vaporisation. 



Too 



27% 



"4% 

 8-1 % 



3-3? 



divided between the two processes had we not known how great is 

 the excess of radiant energy incident on the leaf. But now that we 

 know the available fraction of this total amount, we may try to 

 compare in a rough estimate the quantities of energy absorbed by the 

 leaf with those spent in the chemical work of assimilation as well as in 

 the physical work of chlorovaporisation. 



We admitted that the absorption of the chlorophyll of a leaf amounts 

 to 27 per cent. With the diminution of the total energy of the radia- 

 tion it will fall off in proportion (fig. 10). We have seen further that 



