THE ORIGIN AND ROLE OF PENTOSE SUGARS. 

 OH H H OH H H OH 



79 



COH- 



-CH,OH 



COH- 



H OH OH H 

 D-galactose. 



CH.OH 



OH OH H 

 D-lyrose. 



It is a striking fact, however, that in nature d-glucose has almost always 

 been found with 1-xylose, and that d-galactose is usually associated with 

 1-arabinose. Also, it is noteworthy that the pentose sugars thus found are 

 of the 1- and not of the d- series. These facts speak strongly in favor of the 

 theory of pentose formation here presented. A study of the photolysis of 

 the hexonic acids which is now in progress will throw much light on these 

 reactions. 



Finally, a brief consideration may be given to the significance of such 

 pentosan formation to the plant. A most striking property of the pentosans 

 is their mucilaginous character. They have the power of swelling and 

 taking up an enormous amount of water. This property is not exhibited by 

 the hexose-polysaccharides in nearly so marked a degree. A notable increase 

 of pentosans in the cells would have most important consequences. The 

 enormous imbibition capacity of the pentosans would permit the absorption 

 of large quantities of water at such times when this is available. In other 

 words, the presence within the cell of a hydrophile colloid such as a pento- 

 san makes possible the absorption of large quantities of water. Such, in 

 fact, is the nature and behavior of succulent plants as the cacti. This point 

 is of special interest in view of the fact that the hydrophile colloids in the 

 plants are themselves products of arid conditions, and opens the way for a 

 new conception as to the origin of the morphological character of succulent 

 plants, based upon physiological principles. 



