DEPARTMENT OF BOTANICAL RESEARCH.* 



D. T. MacDougal, Director. 



Most of the problems under consideration are mentioned in the fol- 

 lowing paragraphs, which also indicate methods of procedure, describe 

 progress, and summarize the more important results. 



The study of the available facts and accepted conclusions concern- 

 ing photosynthesis, perhaps the most important single process in the 

 organic world, eliminates the theory of Baeyer from the possible 

 explanations. The experimental research on this subject is planned 

 on the conception that its initial stage is much more complex than a 

 simple condensation of formaldehyde to sugar. 



The cacti have been selected for the study of the carbohydrate 

 economy of plants, and no evidence has so far been uncovered indica- 

 tive of special formative substances. These and other plants may get 

 into a state of starvation for sugar, although having an ample supply 

 of starch on hand which can not be hydrolyzed at temperatures inhibit- 

 ing enzymatic action or when the shoot is in a desiccated condition. 



The lower limit at which certain cacti may begin to grow has been 

 found to vary from 10° to 25° C. in the same plant, and the upper limit 

 at which growth ceases from 26° to 43° C. in a single plant. Tempera- 

 ture coefficients of 2 or more for every rise of 10° C. were found between 

 10° and 30° or 35° C. Maxima of 49° C. for growth were encountered. 

 Endurance of temperatures of 52° and 53° C. were noted. All tempera- 

 tures were those of the plant-body instead of the air, as ordinarily taken. 



The precision auxograph has now been perfected to a point where 

 it will record a change of 0.0004 inch in length or thickness. It has 

 been made in a form suitable for recording growth or shrinkage of 

 plants, imbibition swelhngs, or the swelUng of colloids of interest in 

 connection with growth. 



Eriogonum nudum exhibits a course of growth in which the maximum 

 is in daylight, and the rate is largely determined by the balance 

 between absorption and water-loss, no recognizable inhibiting effect 

 by light being found. 



The screens of special glass have now been developed to a point 

 where they can be manufactured in 16 cm. squares in quantity. 



Imbibition is defined as the distensive force in the earlier stage of 

 growth of the cell, and it plays an important but diminishing part as 

 vacuoles are formed and the protoplast enlarges. Osmosis increases 

 in importance with the development of the cell. Most plant-cells have 

 a greater capacity for water when shghtly alkahne, unlike gelatine, which 

 swells most in acidified solutions. In consequence of this fact acidity 

 checks or retards growth. 



♦Situated at Tucson, Arizona. 



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