DEPARTMENT OF BOTANICAL RESEARCH.^ 



D. T. MacDougal, Director. 



Progress has been made in the principal problems to which the resources of 

 the Department and the energy of the members of the staff and collaborators 

 are directed as detailed in the following paragraphs: 



PHOTOSYNTHESIS AND METABOLISM. 



Photosynthesis, by H. A. Spoehr. 



In the autumn of 1919 experimental investigations were begun to establish 

 definitely whether photosynthesis is a process intimately associated with the 

 vital activity of the plant and thus dependent upon the general protoplasmic 

 metabolism or whether photosynthesis can proceed independently of these 

 activities and simply contributes material essential to the oxidative catabolism 

 and to growth. It was argued that if a direct interdependence exists between 

 the photosynthetic and catabolic activities of the plant, it is to be expected 

 that factors influencing the respiration would then also affect the photosyn- 

 thetic activity. Therefore, an extensive investigation of the respiratory 

 activity of leaves was undertaken with a view of establishing the more essen- 

 tial factors which determine the rate of the oxidative breakdown of the carbo- 

 hydrate fuel material and the relation which these bear to the photosynthetic 

 activity. These investigations have been brought to a conclusion and have 

 been submitted for publication. 



Experimental Methods. 



Extensive preliminary investigations were made to test out the various 

 principles and methods of determining the rates of respiration and of photo- 

 synthesis of land plants. In view of the great complexity of these processes 

 and the large number of factors which must be taken into consideration, the 

 greatest care must be exercised to avoid spurious results, so that the long 

 time which has been put upon these preliminary studies has proved to have 

 been fully warranted. 



For the purposes of these investigations a highly accurate method was 

 developed, based upon the differential determination of carbon dioxid. This 

 gas is absorbed in solutions of barium hydroxide and the concentration of the 

 latter determined by means of the electrical conductivity. Suitable absorp- 

 tion tubes, sedimentation vessels, and electrolytic ceUs have been devised and 

 constructed. The wide range of experimental conditions over which these 

 investigations have been carried, entailing the determination of relatively large 

 as well as of very small quantities of carbon dioxid, necessitated careful check- 

 ing of the degree of accuracy of these methods for each set of conditions. The 

 electrolytic method of carbon-dioxid determination offers far greater flexi- 

 bility than any other method, in that almost any required degree of accuracy 

 can be obtained for widely different experimental conditions by a rational 



' Situated at Tucson, Arizona, and Carmel, California. 



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