I [2 Carbon Assimilation. 



trated hydrochloric acid for 3 hours on a boiling water bath. 

 This results in the hydrolysis of both the cane sugar and maltose, 

 and the increase in cupric-reducing power and change in optical 

 rotation as compared with the numbers obtained after inversion of 

 cane sugar, give the quantity of maltose. 



The cupric-reduction and optical rotation methods do not give 

 concordant numbers for maltose. Davis and Daish (1913) suggest 

 that this is due to the destruction of fructose. 



(iv.) The cupric-reducing power and optical rotation of the 

 original purified extract not accounted for by sucrose and maltose 

 are due to glucose and fructose, the quantities of which can be 

 calculated from these values. We discuss the reliability of the 

 glucose and fructose numbers later (pp. 113-114). 



(c) Method of Davis, Daish and Saivyer. These workers 

 estimate sucrose, maltose, glucose, fructose and pentoses. Their 

 methods are essentially the same as those of Brown and iVlorris, 

 but they eliminate several sources of error and introduce some 

 important modifications. 



(i.) As with previous workers the cupric-reducing power and 

 optical rotation of the purified extract is measured. The cupric- 

 reduction is due to glucose, fructose, maltose and pentoses. 



(ii.) For the estimation of cane sugar the solution is inverted 

 with dilute acid or invertase. But Davis and Daish (1913) find that 

 with 2% citi'ic acid, inversion of cane sugar is not complete in plant 

 extracts. For this reason they conclude that the earlier results of 

 Campbell (1911), for example, must be completely withdrawn, as an 

 error in the estimation of cane sugar results in an error in maltose 

 and hexoses as well. In the case of Parkin's experiments, however, 

 they consider that any error arising from this cause was small. 



Davis, Daish and Sawyer therefore invert the slightly acid 

 solution by boiling it with 10% citric acid for 10 minutes, or by 

 treating it with 1-2 c.c. autolysed yeast (containing invertase) for 

 24 hours at 38"-40"C. The increase of reducing power or the change 

 of optical rotation both give the quantity of sucrose present. As the 

 two numbers da not give approximately the same value for sucrose, 

 it is assumed that there are optically active substances other than 

 sugars which vitiate the values obtained from optical rotation data. 

 The values obtained by cupric-reduction are therefore the ones 

 assumed to give the true value for cane sugar. 



(iii.) In order to estimate maltose, the lead in the extract (p. Ill) 

 is completely removed by treatment with hydrogen sulphide. The 

 excess of this is removed with ferric hydroxide. The solution 



