DEPARTMENT OF BOTANICAL RESEARCH. 



83 



oxalic acid is very easily decomposed in the light, small amounts 

 daily unite with calcium to form an insoluble and pliotochemically 

 stable compound within the cell. It was found that on diminution 

 of the total acidity of Opuntia versicolor joints and other richly acid 

 cacti the amount of volatile acids increased. The formation of the 

 relativel}' photochemically stable acetic and formic acids from malic 

 acid would explain this fact. The observation of Kraus that the 

 rate of decrease of acidity in a succulent diminishes under constant 

 light and temperature conditions can also be explained hereby. The 

 formation of formaldehyde from malic, glycollic, and acetic acids in 

 the light substantiates the criticism that no conclusion can be drawn 

 as to the correctness of the Baeyer hypothesis of carbon dioxide 

 assimilation from the finding of formaldehyde in illuminated leaves. 

 There is some evidence that other plant acids also yield this aldehdye. 

 It is now evident that there are substances formed in the photolysis 

 of plant acids from which sugar can be synthesized by the plant. 

 The results from this study are applicable not only to succulents, 

 but to all green leaves, for the processes and products of the aerobic 

 respiration of sugar are the same in both cases. In the succulent 

 there is simply an accumulation of the malic acid at night, due to an 

 insufficient supplj^ of oxygen. 



Photolytic Effect of Blue-Violet Rays and Their Variations in Solar Radiation, 

 by H. A. Spoehr. 



The biological importance of the blue-violet rays is constantly 

 becoming more evident. A comparison of the results obtained with 

 a Smithsonian Institution pyrheliometer and those obtained with 

 the chemical photometer shows that a knowledge of the total insola- 

 tion (as obtained with the pyrheliometer) is of limited value for the 

 study of climate from a physiological point of view. It has been 

 found that the intensity of the violet raj^s shows sudden and 

 unpredictable variations quite independent of the variations in total 

 intensity. Winter values are decidedly less than those of the summer, 



Results obtained with the Smithsonian Institution pyrheliometer No. 16, means for months 

 indicated, expi-essed in standard calories per square centimenter per minute. 



