82 CARNEGIE INSTITUTION OF WASHINGTON. 



water-columns to begin or to become greater and thus to draw water 

 from other parts of the plant until the intake is nearly equal to the 

 outgo. It is also suggested that the closure of the stomata is caused 

 by a slight drying out of the tissues and thus takes place after the 

 transpiration-rate has been cut down. 



Since, as is well recognized, the transpiration-absorption ratio is 

 the most vital factor governing the occurrence and distribution of 

 plants in desert regions, the facts appearing from this work are 

 surely connected with the success of Parkinsonia as a desert peren- 

 nial. In addition to its seasonal responses, such as the dropping of 

 leaves and the dying of branches, there is this daily response which 

 begins with a closure of the leaflets and is followed several hours later 

 by a decrease in the transpiration-rate while the evaporating power 

 of the air is still increasing. Dr. Forrest Shreve has found that seed- 

 lings of this plant w^ithstand the drought seasons only with diffi- 

 culty, the percentages of deaths being very high during the first year 

 and becoming less each succeeding year. The mesophytic type of 

 foliage and stems of the young plants makes the water-loss from 

 such plants higher than from older ones, and the low mechanical 

 strength as shown by the anatomical structure would probably mean 

 that they could not withstand the earlier stages of drying without 

 losing their turgor. 



The Photolysis of Plant Acids, by H. A. Spoehr. 



A careful study of the photolysis of malic acid and of its products 

 has shown that the changes can be described as follows: 



COOH 



I 2C0.. 



CHo ^ + " 



I —*- GH^ Ctt-s CH3 



CHOH I — *• I ^ I 



I CII.OH CH:0 COOH 



COOH " I 



CHoOH CH.OH CO. 



I — ^ I -> + 



CH:0 COOH CH30H->CH.O-^CH;;Oo->C02 



CH:0 CFI:o/ 



I ^ I 



CH:0 COOH 



I 



COOH CH..0.._>C02 



COOH CO- 



Briefly, the organic acids split off carbon dioxide, the dibasic very 

 much more easily than the monobasic; in the presence of atmos- 

 pheric oxygen, alcohols are readily oxidized to aldehydes, and these 

 in turn to acids. Of special interest is the formation of oxalic acid 

 from acetaldehyde, as this is a possible explanation of the presence 

 of the large amounts of this acid in the succulents. Although free 



