108 Hydration and Growth. 



accompanied by the solution or dispersion of material from the exter- 

 nal part of the sections and by the diffusion of whatever salts or acids 

 might be present in the interior of the mass. Sections 0.25 mm. in 

 thickness swelled 2,420 per cent in water, and material equivalent to 

 200 similar sections, weighing 1.6731 g., placed in water for the same 

 length of time, lost 0.2570 g., or 15 per cent of the total. A similar 

 test of sections composed of 8 parts agar and 2 parts gelatine showed a 

 swelling of 1,684 per cent, with a loss of 18 per cent of the original 

 weight by dispersion or solution in the water. 



Sections of Opuntia swelled in water for 24 hours at 16° to 18° C. 

 lost 7 per cent of the average total dry weight of similar sections. As 

 much of the dry weight is insoluble cell-wall, it is to be seen that 

 the actual percentage of soluble or diffusible material extracted was 

 large, a fact which would readily account for the lessened reswelling of 

 sections. 



A single effort was made to ascertain to what extent the acids are 

 extracted in the hydration of living cell-masses of Opuntia and in dried 

 sections of the same. Determinations by Professor H. M. Richards of 

 the acidity of the water in which fresh slices of the Opuntia were swelled 

 showed that this might be expressed as follows: 10 c. c. solution from 

 dish in which set of fresh sections were swelled in water = 0.44 N/20 

 KOH. 



Dried slices of the above material, when swelled in water 24 hours, 

 gave a solution the acidity of which might be expressed as 10 c. c. of 

 solution = 0.10 N/20 KOH. 



When such sections were immersed in citric acid 0.01 N, the strength 

 of the solution was increased so that at the end of 24 hours the acidity 

 was expressible as 10 c. c. of solution = 2.25 N/20 KOH.^ 



The extraction of acid from the fresh sections in water is marked 

 and is much greater in the acid solution. This action in setting 

 free the amino-acids would cause a loss in hydration capacity which 

 would become apparent on reswelling. 



The chief interest in the present work is centered in the hydration 

 of protoplasm associated with growth The development of embryonic 

 cells from the stage of a highly granular, dense colloidal mass with a 

 large nucleus to maturity is characterized by the migration of pro- 

 teinaceous material from the nucleus into the remainder of the mass; 

 by the formation of syncretic cavities, including those designated as 

 vacuoles; and by a constantly varying metabolism which results in 

 continuous alterations in the composition of the vacuolar fluids, and 

 in the composition and hydration capacity of the protoplasm.^ 



The peripheral part of the colloidal mass is probably of greater 

 density than the interior, and it is the behavior of this layer which 



^ MacDougal, Richarde, and Spoehr. The basis of succulence in plants. Bot. Gaz., 67:406. 

 1919. 



' See Thoday, D. On turgescence and the absorption of water by the cells of plants. The 

 New Phytologist, 17: 108. 1918. 



