PENTOSE SUGARS IN PLANT METABOLISM 369 



ucts of the pentoses, (C5H10O5) and that subsequently the CoHg 

 is condensed to the rubber-hydrocarbon (CioHie)x. 



Reducing actions are by no means uncommon in plants, es- 

 pecially as the products of intra-molecular respiration and spe- 

 cial types of fermentation. A well known example of the forma- 

 tion of a hydrocarbon is the production of methane from cellu- 

 lose and pentosans by an anaerobic bacillus.^ 



Harries' conception is further substantiated by the fact that 

 the degradation of caoutchouc yields levulinic acid and levulinic 

 aldehyde which are the same products yielded by the sugars. 



In the light of the foregoing it seemed therefore not without 

 interest to determine whether a plant which is actually produc- 

 ing rubber would show a condition of its carbohydrate content 

 which might tend to substantiate this theory. The desert rub- 

 ber plant, guayule, (Parihenium argentaium) , offered excellent 

 material for such an investigation. The analyses show that in 

 the youngest parts of the plant, in which the rubber is being 

 formed, an unusually high percentage of the total sugars is in 

 the form of pentoses. To the terpenes and their almost in- 

 numerable derivatives belong many of the most important plant 

 products, more especially many of the essential oils, camphor 

 derivatives, etc. 



The pentoses have been known for a long time to be common 

 components of the walls and vessels of plants. The several 

 attempts at making alcohol on a commercial scale from wood 

 have not been very successful, apparently because a considerable 

 percentage of the sugar produced by hydrolysis of the wood is 

 unfermentable. The constitution of cellulose, however, has 

 not yet been clearly established and the way in which the pen- 

 tose molecule is united with the other sugar groups is still 

 unsettled. 



It has long been known that when starch is hydrolysed all of 

 it does not go over into glucose, as is commonly supposed, but 

 there always remains an unfermentable residue. The nature of 

 this residue has been the subject of repeated investigation with- 



» Omlianski, W., Zentr. Bakt. II, 8, 193, 1902. Koch, Jahresber, 14: 457, 

 1903. 



