92 BOTANICAL GAZETTE [January 



conditions. From the cool and humid winter to the hot and dry fore-summer 

 the water content of normal species of Opuntia may change from about 80 to 

 65 per cent, and then rise again to 8s per cent during the humid but hot mid- 

 summer. "Low water-content and high temperatures are associated with: 

 (1) increase of polysaccharides; (2) decrease of monosaccharides; (3) increase 

 of pentosans. High water-content and lower temperatures are associated w r ith: 

 (1) decrease of polysaccharides; (2) increase of monosaccharides; (3) decrease 

 of pentosans. " The author points out the significant fact that "the greatest 

 activity of the plant comes at a time when the content of monosaccharides and 

 disaccharides is highest/' in March and April, although he is careful to state 

 that a relatively large supply of simple sugars is not the only prerequisite for 

 growth, but is only one of many factors. 



In an arid atmosphere the cut joints undergo considerable decrease in 

 water content, while still remaining normal in appearance and activity. The 

 loss of water by transpiration and evaporation is partly compensated for by 

 the water formed in the combustion of sugars, and partly by the condensation 

 of the simple sugars into polysaccharides. Under drought the former decrease, 

 while the latter and the pentosans increase, in total amount. The author 

 suggests that the great imbibitional force of the pentosans may prevent the 

 use of water for hydrolytic processes, when water becomes scarce in the tissue. 

 These phenomena are closely correlated with temperature effects, when the 

 latter are studied independently of varying moisture supply. Enzyme 

 equilibria are discussed in connection with these two factors. 



During the night the succulents respire sugar to acids, principally malic. 

 This is not accompanied by an accumulation of alcohol. In an oxygen-free 

 atmosphere, however, there is much less acid formed, and a very considerable 

 amount of alcohol produced. One molecule of malic acid furnishes two of 

 carbon dioxide and one of ethyl alcohol. Under these anaerobic conditions 

 more sugar is consumed per unit of energy than under aerobic conditions. 

 This is accompanied by an increase in the water content of the tissue. 



During starvation the joints of Opuntia maintain the same relative pro- 

 portions of the various carbohydrates. This disproves the theory that the 

 pentoses are waste products of metabolism, since then they would show an 

 increase. The water relations of the tissue during starvation and during periods 

 of feeding on sugar solutions are discussed at some length. 



Spoehr advances the theory that the pentoses may be formed from 

 glucuronic acid by the loss of a molecule of carbon dioxide, and discusses the 

 isomerism relations between the hexoses and the corresponding pentoses that 

 would be formed through the intermediary of glucuronic acid. — J. J. Willaman. 



Transpiration in tropical rain forests. — The lack of experimental data as 

 to the conditions of plant growth and activity in tropical rain forests is appar- 

 ently leading to some desirable investigation. A notable contribution in this 



