DEPARTMENT OF BOTANICAL RESEARCH. 63 



content is reduced and, vice versa, an increase in water-supply results 

 in a relative increase in these sugars. Pentosan formation is also 

 dependent upon the water-content of the plant. With continued low 

 water-content the pentosans increase decidedly, whereas an ample 

 supply of water results in the reduction of the amount of pentosans. 

 In the aldose monosaccharides the first carbon atom, or the carbonyl 

 group (CH: 0), is the most reactive and is largely responsible for the 

 great reactivity of these sugars. In the disaccharides and poly- 

 saccharides found in these plants this active carbonyl group is so 

 united with other groups that it no longer forms the point of attack 

 in chemical reaction. These sugars are therefore first affected on the 

 opposite end of the chain of carbon atoms, at the CH2OH group. 

 Such a reaction results in a primary formation of glucuronic acid, 

 CH : • (CH.0H)4C00H. This substance has been found as a product 

 of carbohydrate metabolism in animals, usually in the conjugated 

 form. It has now also been found in the extract of the cacti, though 

 only in very small amounts. Its presence is especially significant in 

 that it indicates the mode of pentose formation in these plants. A 

 very general property of acids of this character is the loss of CO2 in 

 the sunlight, and conversion into the corresponding lower aldehyde. In 

 this manner glucuronic acid would form 1-xylose. Neuberg (Ergebuisse 

 d. Physiol. 3: 373, 1904) has actually obtained 1-xylose from glucuronic 

 acid by bacteriological methods. 



Further evidence in favor of this interpretation of the formation 

 of pentoses is obtained from the consideration of the structural relations 

 of the various sugars concerned. If the pentoses were derived from 

 the direct oxidation of the hexoses, d-glucose would yield d-arabinose, 

 and d-galactose would give d-lyxose. It is a striking fact, however, 

 that d-glucose has almost always been found together with 1-xylose, 

 and d-galactose associated with 1-arabinose. This is precisely what 

 would be demanded by the theory of the intermediate formation of 

 glucuronic acid. Final evidence will be obtained from a study of the 

 photolysis of glucuronic acid and other hexonic acids which is now 

 under way. 



Gas Interchange in Mesembryanthemum and Other Succulents, 

 by H. M. Richards. 



Work was continued on the gas interchange and acidity of the 

 species of Mesembryanthemum and Dudleya, which are native in the 

 region around Carmel, California. In their natural habitat these 

 forms do not, owing to the equable climatic conditions, show a very 

 striking periodicity; nevertheless, even when the acid content is 

 relatively stationary, the ratio of carbon dioxide evolved to oxygen 

 absorbed is very low. To account for this is the problem at hand 



