The Carbohydrates of the Leaf. 103 



and£l=!!<l 

 u — a 



we have 1— -> — (m— 1) 

 d d 



Now 1 — - is the difference between the real assimiiatory 

 coefficient and unity and ^(m— 1) is actually not greater than 0-01 



in the first case, nor less than — 0-01 in the second. Hence the 

 real assimiiatory coefficient differs from unity by a quantity less 

 than 001. 



From the results we have collected together in this section it 

 becomes quite clear that the relation between the oxygen evolved 

 in assimilation and the carbon dioxide taken in, is by no means 

 definitely determined. Yet this is a matter of great importance 

 in regard to the problems of carbon assimilation, for in the determin- 

 ation of the nature of a reaction or series of reactions, it is of first 

 importance to know the quantitative relation between the initial 

 substances and the products of the reactions. 



C. The Cahbohydrates of the Leaf. 



The presence of starch in the leaf was recognised by von Mohl 

 as long ago as 1837, but it was Sachs (1862, 1864) who identified 

 this starch as a product of assimilation by showing tiiatit appeared 

 in the chloroplasts after exposure to light and disappeared in the 

 dark, and he also showed that chlorophyll was necessary. Sachs' 

 conclusion that starch produced in the chloroplast is the first 

 visible product of assimilation is well known. The method of 

 detection of starch by decolorisation of leaves by alcohol and 

 subsequent treatment with an alcoholic solution of iodine is still the 

 current method of detection of starch in the plant. 



It was later recognised that many leaves never elaborate starch 

 and A. Meyer (1885) classified plants into classes according to the 

 quantity of starch their leaves contain. Leaves forming little or no 

 starch were known to yield extracts which reduced cupric solutions 

 and which were optically active, and it was therefore concluded that 

 such leaves contained reducing sugars. In addition the non-reducing 

 disaccharide cane sugar was actually extracted in a crystalline form 

 from leaves of Vine by Kayser (1883). 



Brown and Morris (1893) justly pointed out that there was no 

 proof that the cupric reducing substances in the leaf were sugars, 

 and they therefore tested for different sugars. They state that the 



