DEPARTMENT OE BOTANICAL RESEARCH. 65 



atmometer), leaf-temperature, and stomatal movement. Water-content de- 

 terminations were made on young hothouse-grown plants, on outdoor 

 seedlings, and on tips, branches, and trunks of trees, and the results are to 

 be compared with the transpiration curve. 



In connection with this work, methods have been developed for (i) meas- 

 urement of transpiration of outdoor plants in situ under controlled conditions 

 in shade and in sunshine; (2) measurement of leaf temperature; (3) prepa- 

 ration of the leaf as a whole for stomatal examination. 



Chemical Effects of Radiant Energy in Plant Processes, by Dr. H. A. Spoehr. 



Extensive experiments in photochemical reactions supposedly similar to 

 those occurring in plants have been carried out in the Kent Chemical Labora- 

 tory of the University of Chicago during the past year. It has been found 

 that aqueous solutions of potassium and calcium nitrates are reduced by 

 means of ultra-violet light, sunlight, and even diffuse light, to the correspond- 

 ing nitrites and ammonia, with the liberation of oxygen and the production 

 of alkalinity in the solution. Schimper has shown that the disappearance of 

 nitrates in the leaf takes place especially in the sunlight. If, therefore, the 

 above reaction is actually the one taking place in the leaf, not only would the 

 proper conditions for carbohydrate synthesis be established, but the nitrogen 

 would also be produced in the best form and in the most available place for 

 protein synthesis. That this is the actual fate of nitrates in the plant has not 

 yet been proved, but it seems highly probable on theoretical grounds. 



The production of an alkaline locus in the plant leaf has further impor- 

 tance, since from theoretical considerations it is highly probable that carbonic 

 acid is reduced in the form of the potassium hydrogen salt in the early stages 

 of photosynthesis. 



The role of organic acids in the plant leaf and the relation of these sub- 

 stances to protein synthesis are under investigation. It has been found that 

 the hydroxy-acids, under the influence of ultra-violet light, are decomposed, 

 yielding CO2 and aldehyde-like substances. These, of course, may be very 

 important in the further synthesis of compounds of importance to the organ- 

 isms. The effects in question may concern both photosynthesis as indicated 

 and may also be associated with respiratory changes in the acids as dis- 

 covered by Richards and described in another section of this report. 



Some other remarkable reactions of organic substances under ultra-violet 

 light will be discussed later. 



The admirable conditions of sunlight at Tucson will be useful for the 

 further study of these photochemical changes, and it is hoped also to devise 

 some practical method of determining the phases of the energy of light which 

 have special importance to vegetation. 



