DEPARTMENT OF BOTANICAL RESEARCH.* 



D. T. MacDougal, Director. 



The activities of the year have been rewarded by definite progress 

 in the study of all of the groups of problems under consideration. Some 

 of the more important results may be briefly suiiunarized as follows : 



Growth in plants takes place at the expense of definite or formative 

 compounds, which are formed locally at a rate determined primarily 

 by the influence of temperature on chemical velocity. These construc- 

 tive processes may be masked or checked by imperfect respiration, and 

 enlargement depends upon conditions favorable to water-absorption. 

 Light breaks down the smothering acids resulting from incomplete 

 respiration in cacti and thus facilitates the construction of formative 

 material. The lessened acidity resulting from the action of light is a 

 condition of increased absorption of water, so that light may accelerate 

 growth in two different ways. 



Improvements in auxographic instruments and the designing of 

 glass screens of specialized transmissibility of light have been accom- 

 plished. 



The readily varying permeability of protoplasm is referred to the 

 interrelations of the disperse-phase and disperse-medium of the hydro- 

 phile emulsion colloids of which it is made up. 



Repetition of the experiments upon respiration with temperature 

 controlled to within 0.02° C. demonstrates conclusively^ that sunlight 

 causes changes in the air, as a result of which respiration (as measured 

 by excretion of carbon dioxide) is highest on days of high solar radiation, 

 less on cloudy days, and least at night. Arrangements are being made 

 for measurements of the electrical conditions of the air under identical 

 conditions. 



In the study of the possible phases of photosynthesis in plants solu- 

 tions of carbon dioxide and potassium carbonate have been reduced to 

 formic acid by exposure to light from a mercury- vapor arc in a quartz 

 tube. Next a sugar-like substance has been obtained by exposure of 

 formic acid to sunlight and to ultra-violet light. This substance gives 

 the reactions of sugar and can be used as food by green algse in darkness. 



Succulent plants desiccated for long periods may show normal pro- 

 portions of water-content, owing to the coincident respiration or oxida- 

 tion of solid material. 



The hydrolyzable carbohydrates of such plants starved for periods 

 of one to six years were decreased, but the proportion of non-reducing 

 sugars increased during starvation. Hydrolysis of cell-walls, deforma- 

 tion and peripheral thickening of the nuclei, and reduction of the 



♦Situated at Tucson, Arizona. 



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