68 THE CARBOHYDRATES 



Both mannose and galactose are sometimes considered to 

 be transitory substances ; an idea supported by the fact, ob- 

 served by Herissey,* that seminase is found in the seeds of 

 lucerne ; and that during germination cane sugar is relatively 

 abundant, while mannose and galactose are not found, at any 

 rate in any quantity. 



DISACCHARIDES. 

 CANE SUGAR, SUCROSE OR SACCHAROSE. 



Cane sugar is one of the most widely distributed substances 

 to be found in the vegetable kingdom. Besides forming about 

 20 per cent of the juice of the sugar cane, SaccJtarum officinarum, 

 and about IO to 20 per cent of that of the beetroot, it is found 

 in varying quantities in the wood of maple and birch, and in 

 Sorghum saccharatum ; it occurs, moreover, in wheat, maize, 

 barley, in carrots and in madder root. In most sweet fruits 

 it is found together with a greater or lesser quantity of dextrose 

 and levulose, which may possibly have been formed from it 

 by hydrolysis. It also is found in the leaves of many plants 

 associated with glucose and maltose. The following table, 

 compiled by Kulisch, gives the relative proportions of cane 

 sugar and hexoses found in various fruits. 



Cane Sugar. Hexoses. 



Pine apple . . ii'33 1*98 



Strawberry . . 6-33 4-98 



Apricot . . . 6-04 2' 74 



Ripe banana . . 5-00 io'oo 



Apple . 



1-5-40 



In honey practically only invert sugar f is found, although the 

 sugar found in the flowers by the bees is commonly cane sugar. 

 The hydrolytic agent in this case is, however, most probably 

 the formic acid secreted by the bees. 



The two chief sources for the preparation of cane sugar on 

 a manufacturing scale are the sugar cane and the beet. The 

 processes used in both cases are more or less similar, and con- 

 sist in obtaining the juice, purifying it, concentrating it and, 

 lastly, crystallizing it. The juice is generally obtained from 

 the cane by crushing, as much as 85-95 per cent of the juice 



* He'rissey : " Rev. gen. Bot.," 1903, 15, 345, 369, 406, 444. 

 t A mixture of dextrose and levulose, see p. 64. 



