194 



BOOKS AND CURRENT LITERATURE 



however, and in closing the reviewer believes he is expressing the senti- 

 ment of a large number of pathologists when he states his appreciation 

 of the excellences and value of the book. — Ernest Shaw Reynolds. 



Acidity in Cacti. — The subject of the diurnal fluctuation of acidity 

 in succulents has recently been treated from the chemical standpoint 

 by H. A. Spoehr.'^ A number of conclusions are reached, among which 

 the following are of most interest to botanists. 



1. After oxalic acid, malic acid is of most frequent occurrence in 

 plant tissues. 



2. In Opuntia versicolor the highest acidity was found just before 

 sunrise when 1 cc. of expressed juice was equivalent to 2.45 cc. tt 

 potassium hydroxide, while the lowest was five hours after noon when 

 1 cc. of juice was equivalent to 0.31 cc. t'o hydroxide. 



3. The expressed juice of cacti showed decrease of acidity with 

 evolution of oxygen, m vitro when placed in sunlight or in the light of 

 a mercury vapor lamp. 



4. Increase of acidity in plants takes place under conditions of oxy- 

 gen scarcity. Succulents have poor aeration within their tissues and 

 hence a greater accumulation of acid takes place in them than in other 

 plants. The process, however, occurs in all plants. 



5. The reactions concerned in the photolysis of malic acid were 

 proved to be as follows : 



COOH 



CH2 



CHOH 



COOH 



2CO2 

 -> + 

 CH3 



CH3 



CH3 



CH2OH Cf O COOH\^ 



CH2OH CH2OH CO2 



CH:0 COOH CH3OH -^ CHgO -»CH202 



\ 



\ CH:0 CH:0 



\ 



CH:0 COOH 



i 

 COOH CH2O2 



I — ^ + 

 COOH CO2 



CO2 



iSpoehr, H. A., Photochemische Vorgange bei der diurnalen Entsauerung 

 der Succulenten. Biochem. Zeitschr. 57: 95-111, 1913. 



