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AUXOGRAPHIC MEASUREMENT OF SWELLING OF 



BIOCOLLOIDS AND OF PLANTS 



D. T. MacDougal 



(with two figures) 



The chief purpose of this article is to describe the methods 

 which have been used in the study of colloidal preparations, the 

 reactions of which might furnish a physical basis for the interpre- 

 tation of growth in plants, and to recapitulate some of the features 

 of swelling of these substances as yet undescribed or but little known. 



The investigation of growth in plants involves a measurement 

 of the unsatisfied hydration capacity of living cell masses, and 

 also determinations of the total swelling capacity of desiccated 

 material. In both cases the minute masses of colloids constituting 

 the protoplasts are inclosed in thin walls with a low stretching 

 coefficient. Furthermore, the living cells are in a condition of 

 varying turgidity, dependent upon the osmotic activity of the 

 vacuolar solutions, upon the permeability of the external layer of 

 the protoplasm, and also upon the structure of the walls. Desic- 

 cated cell masses have lost the capacity of turgidity as ordinarily 

 known, but may still show some osmotic activity by the differential 

 action of the dead wall (as may other colloids), while the proto- 

 plasts have undergone changes due to the action of salts and acids 



in the concentration of cell saps which accompanies desiccation. 



It is not possible to reproduce the mechanical structure of cell 

 masses by artificially compounded biocolloids, so the experimenter 

 must be content to ascertain the general composition of the proto- 

 plasm, bring the main constituents together in the form of a jelly, 

 dry this to thin plates, and measure the action of sections of it in 

 solutions of a kind and concentration which would give effects 

 similar to those encountered in living matter. 



Physiologists concerned with life in animals 



dealing with a 



protoplasm consisting chiefly of proteins and lipins with a charac- 

 teristic metabolism, have found in gelatine and in the soaps material 











Botanical Gazette, vol. 70] 



[126 







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