126 Carbon Assimilation. 



that the sucrose is translocated away from the leaves in the form 

 of hexoses. 



Even in this plant where the leaves contain abundant starch 

 no maltose is found, either in the leaves or petioles. Davis and 

 Sawyer therefore conclude that the starch, on utilisation by the 

 plant, is bi'oken down into hexoses by a mixture of enzymes similar 

 to that of Aspergillus oryzce which yields taUa-diastase. They 

 consider that dextrin and maltose are intermediate stages in the 

 degradation of starch to glucose. Dextrin indeed appears at the 

 period when starch is in large quantity in the leaf. They suppose 

 the enzyme maltase is always present in relative excess in the leaf, 

 and Daish (1916) has shown the presence of maltase in a number 

 of different leaves. 



5. Vine (Vitis vinifera). 



In the leaf of the vine, a plant which stores its carbohydrate 

 as glucose, Deleano (1912) was unable to detect sucrose in the leaf. 

 Davis and his co-workers, on the other hand, state that after taking 

 special precautions in sampling to prevent the leaf enzymes from 

 acting, sucrose is found to be the principal sugar of the leaf. This 

 they regard as supporting their view that sucrose is the first sugar 

 formed in assimilation. 



F. Carbohydrate Transformations in the Leaf. 



The pioneer researches of Sachs indicated the formation of 

 starch in the chloroplasts of the leaf as a result of carbon assimilation, 

 and it was this investigator who showed the dependence of starch 

 formation on light and chlorophyll. The proof was completed by 

 Godlewski (1873) and Pfeffer (1873) who showed the necessity for 

 an outer atmosphere containing carbon dioxide. 



Sachs held the view that starch was the first visible product of 

 assimilation, and he bound himself to no theories concerning 

 possible intermediate products in its formation. 



Kayser's work (1883) established the presence of sucrose in 

 the leaf of the vine. It was supposed that starch was converted 

 into cane sugar by diastatic enzymes and that the cane sugar was 

 inverted in the conducting tissue of the leaf. Sachs (1884) also 

 expressed the opinion that the starch is translocated in the form of 

 sugar. 



That starch could not always be the first visible product of 

 carbon assimilation became obvious from the researches of A. Meyer 

 (1885) who sho^ved that different species varied greatly in their 



