252 PHYSIOLOGY LBot. Absts. 



to be one of the factors necessary for growth. Series of experiments in which either the 

 temperature or water conditions were altered show that low water content and high tem- 

 perature affect the carbohydrate equilibrium in the same direction, and in reverse manner 

 as related to high water content and low temperature, as just indicated. — In dry seasons loss 

 of water and resultant need of water by the plant causes condensations of monosaccharides 

 and disaccharides into polysaccharides and pentosans. Water is also formed by oxidation of 

 simple sugars in respiration. Simple sugars quickly disappear when the plant undergoes 

 natural or artificial slow desiccation. These plants can continue to live for a long time with- 

 out water or formation of food and with but slight change in the per cent of water. These 

 plants were kept at 28°C. in the dark for 189 days, they lost over 60 per cent in weight, and 

 the water-content was reduced by but 12 per cent. The carbohydrate metabolism under 

 these conditions is also treated.— The nocturnal respiration of cacti is characterized by the 

 formation of acids due to restricted oxygen supply. No accumulation of alcohol was found 

 during the night but a distinct increase was observed after the plants had been exposed to 

 sunlight for some time, probably due to disintegration of malic acid: 



COOH • CH 2 • CHOH ■ COOH — > 2 C0 2 + CH 3 • CH 2 OH 



Under anaerobic conditions there is a very active production of alcohol but little acid for- 

 mation in cacti. Under these conditions there is also higher rate of carbohydrate consump- 

 tion and water formation than in air. The plants do not go into a condition of dormancy 

 when the water supply is greatly diminished, but continue their normal respiratory activity, 

 this being possible by virtue of their ability to use as food material not only the simple mono- 

 saccharides but also the polysaccharides, and results in the formation of pentosans. The 

 simpler sugars, or monosaccharides, decrease in amount in the plants as the water 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 re- 

 sponsible for the great reactivity of these sugars. In the disaccharides and polysaccharides 

 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 CH 2 OH group. Such a reaction results 

 in a primary formation of glucuronic acid. CH: 0(OH>OH).iCOOH. 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 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 conver- 

 sion into the corresponding lower aldehyde. In this manner glucuronic acid would form 

 1-xylose. Neuberg (Ergebnisse 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-xylose. It is a 

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

 and d-galact.oH ■ associated with 1-arabinose. This is precisely what would be demanded by 

 the theory of the intermediate formation of glucuronic acid. — J. M. McGee. 



METABOLISM (NITROGEN RELATIONS) 



1745. Fosse, R. Le mecanisme de la formation artificielle de Puree par oxydation et la 

 synthase des principes naturels chez les vegetaux. [The mechanism of artificial formation of 

 urea and the synthesis of substances in plants.] Compt. Rend. Acad. Sci. Paris 168: 1164- 

 1166. 1919. — The author finds that formaldehyde and hydrocyanic acid are intermediate 



duel in the formation of urea. It is suggested that there may be some relation between 

 the synthesis of urea and the synthesis of glucose in plants. — V. II. Young. 



