262 The Carbohjidrates of tin- MaiKjold Leaf 



sugars. According to Pellet the reducing sugars which are found in the 

 juice of the crushed cane are present as such within the cane itself and 

 are not formed by inversion of the expressed juice. The proportion of 

 reducing sugar to cane sugar increases on passing from the lower to 

 the upper parts of the caue — that is nearer to the leaves ; it grows less 

 and less as ripening proceeds, pointing to a conversion of the reducing 

 sugars into saccharose. Colin [1914] takes a similar view to Pellet. 

 He shows that Girard's and Strohmer's assertions that reducing sugars 

 are absent from the root of the beet are quite incorrect, especially in the 

 early stages of growth, when the reducing sugar may form 20 per cent, 

 of the total sugars. As the root develops and the store of cane sugar 

 increases in it, the proportion of reducing sugar naturally falls, but it 

 never entirely disappears and is always most abundant in the growing 

 parts. In the neck the ratio of reducing sugar to cane sugar is highest. 

 The root therefore receives at the same time both cane sugar and 

 reducing sugars : the former is stored up and the latter polymerised to 

 cane sugar. The entry of the sugars is regulated by the osmotic pressure 

 of the mixture. 



The recent work of Campbell [1911] and Kluyver [1914] will be dealt 

 with later. 



Experimental. 



Methods of Work. 



Destruction of enzymes. Much of the earlier work on the carbo- 

 hydrates of the leaf is of doubtful value because insufficient care was 

 taken to ensure that no change in the carbohydrates should occur after 

 the picking of the leaves and during the preparation of the sample for 

 analysis ; changes brought about by enzymes are, as we shall show, very 

 Hable to occur either during the process of drying the leaf or during 

 the expression of the sap, if a press be used. Whilst it is possible to 

 express the juice from the root of the beet or mangold, or from the sugar 

 cane, without nuich change in the cane sugar occurring, owing to 

 enzymes being almost entirely absent in such cases, with leaf tissue 

 such a process is unsafe, as enzymes are present in relatively large 

 amount and are liberated from the rolls in which they are contained 

 by the mechanical pressure and thus have an opportunity to act upon 

 the sugars during the time taken in preparing the sample. The work 

 of (iirard [1884] in particular, although he states that he worked as 

 rapidly as possible, was liable to error from this cause; the leaves of 



