DEPARTMENT OF BOTANICAL RESEARCH.^ 



D. T. MacDougal, Director. 



Progress in the development of the various subjects under considera- 

 tion by members of the staff, assistants, and collaborators is adequately 

 described in the following paragraphs, and in the interest of brevity 

 no general summary is presented. 



Conditions have operated to restrict field work during the year. 

 All important stations as far eastward as the Graham Mountains, 

 the Grand Canyon, and the Colorado River on the westward have 

 been visited from the Desert Laboratory. 



IMBIBITION AND WATER-RELATIONS OF PLANTS. 



The Construction of a Biocolloid exhibiting some of the Water-Relations of 

 Living Plants, hy D. T. MacDougal. 



A complete representation of protoplasm would doubtless reveal it 

 as a very intricate complex of material which might be separable into 

 a large number of substances or definite chemical compounds. The 

 greater number of such substances would be seen to be of such nature 

 that their formation, disintegration, or change would not be accompa- 

 nied by much variation of the volume of the water included or held. 



Growing protoplasts contain 98 per cent or more of water, and any 

 inquiry as to the physical basis and chemical processes implied in 

 growth would therefore be logically directed toward the substances 

 which may adsorb and hold large proportions of water. This natu- 

 rally focuses attention on the comparatively inert pentoses of the 

 plant-cells as the basis of imbibition phenomena. Pure amorphous 

 carbohydrate does not exist in the organism; it is always mixed with 

 albumen and some of its derivatives, necessarily includes salts, and is 

 continuously modified by respiration or other metabolic process, accom- 

 panied by varying states of acidosis or alkalosis. 



The above assumptions have been used as a basis for experimenta- 

 tion for the purpose of constructing a mixture of colloids which would 

 exhibit the imbibitional but not the osmotic phenomena of the plant. 



Agar has been taken to represent the amorphous carbohydrate 

 element, and to it have been added albumen, amino-acids, amides, and 

 other compounds. Salts have been incorporated in the mixtures or 

 dissolved in the solutions used to produce swelling. 



Solutions of various mixtures were poured on glass plates in layers 

 about 1 cm. thick and 3 by 5 cm. in area. Desiccation resulted in a 

 reduction to a thickness of 0.1 to 0.3 mm. usually. The principal 



^Situated at Tucson, Arizona. 



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