1 84 THE CARBOHYDRATES 



are not directly extractable by boiling with water, and 

 occur in the wood in such combination that they are only 

 soluble in water after precipitation from the alkaline solution 

 with which they were extracted from the wood. There is 

 a good deal of variation in the composition and properties of 

 the various wood gums ; thus while hard woods may contain 

 up to 20 per cent of xylan, the wood of gymnosperms con- 

 tains only about i per cent of this substance but contains, 

 on the other hand, galactans * ; amounts of galactan varying 

 from 8-17 per cent have been found in Larix occidentalis.'\ 



According to Schorger and Smith % this substance is 

 characteristically associated with coniferous wood, though it 

 has also been reported in the wood of angiosperms such as 

 aspen, white oak, and apple ; it is not certain whether all 

 these woods contain the same galactan. The so-called 

 e-galactan which occurs in the wood of Larix orientalis, to 

 the extent of about 8-17 per cent, is a white powder which 

 dissolves readily in cold water, and in this respect bears no 

 true resemblance to a gum. 



GALACTAN. 



The term galactan is apphed to any non-reducing substance 

 which on hydrolysis gives rise to galactose ; while the plant 

 world supplies a great many substances which yield galactose 

 on hydrolysis, the number of such substances which yield this 

 sugar only, unaccompanied by other sugars, is small. 



A number of other galactans have from time to time been 

 described as occurring in the seeds of lucerne, lupin, and in 

 beets ; these are ill-defined substances which in the past 

 have been distinguished by prefixing letters of the Greek 

 alphabet to the term galactan, but the present state of our 

 knowledge concerning them does not justify a fuller description. 



* Schorger and Smith : " J. Ind. Eng. Chem.," 1916, 8, 494. 



t This fact has been commercially exploited in America for the manu- 

 facture of raucic acid by the oxidation with nitric acid of hydrolysed 

 sawdust ; the galactan has also been recommended as a source of alcohol. 



I Schorger and Smith : " J. Ind. Eng. Chem.," 1916, 8, 494. 



