DEPARTMENT OF BOTANICAL RESEARCH. 55 



solution, in reverse of the action of the CaCU sokition, which was 

 greatest but still less than in water until at 0.0001m. Swelling in 

 KCl did not exceed that in water until a concentration of 0.01m was 

 reached. 



The maximum swelling of a gelatine (3 parts) -agar (2 parts) plate 

 is greatest in HCl O.OIn, KCl 0.001m, and CaCla at 0.0001m. 



Different ecological types of roots of maize show different hydra- 

 tion reactions to the solutions used in hydration tests of colloids, as 

 noted in the foregoing paragraphs. 



Roots of strawberry show differing hydration reactions when 

 grown in saline soils and in sand. 



Roots of orange seedlings show lessened hydration in acid solutions, 

 and their hydration was lessened in all solutions except balanced solu- 

 tions of sea-water and of sodium and calcium chloride. 



Swellings of sections of joints of Opuntia were greatest in KOH at 

 O.OlN, HCl at O.OOlN, and KCl at 0.0001m, all producing effects in 

 excess of the swelling in water. 



The changes in volume of living cell-masses in hydrating solutions 

 include osmotic-plasmolytic effects in the alterations of the volume 

 of the included cells. The hydration of dead cell-masses includes 

 possible osmotic action of cell-walls. 



The hydration reactions described in this paper may include coagu- 

 lation effects when the higher concentrations were applied to the bio- 

 colloids, similar to those of the plasmatic colloids. Actual effects of 

 balanced solutions are clearly defined in the hj'dration of agar, and 

 some suggestions of similar action in the biocolloids arise from the 

 measurements of swelling of the biocolloids described. 



Effects of Age and of the Inclusion of Salts on the Heterotropic Action of Col- 

 loidal Bodies of Cytological Interest, by D. T. MacDougal. 



Auxographic measurements of the swelling of sections of dried 

 plates of agar and of gelatine previously described show that the 

 relative enlargement of a colloidal body in its different axes will be 

 determined largely by the unequal stresses which may be set up, as, 

 for example, when liquid agar or gelatine is poured on glass and dried 

 without shrinking in area. It was pointed out that sections from 

 such plates of agar increased only 3 or 4 per cent in length while swell- 

 ing 3,000 or even 4,000 per cent in thickness, and tliat sections of gela- 

 tine increased 8 to 40 per cent in length while swelling from 500 to 

 2,000 per cent under the auxograph. 



Tests of sections of plates of pure agar freshly made and a year old 

 have been made. Plates which swelled 2,000 per cent in water when 

 freshly made August 1, 1919, increased but 1,600 per cent July 1, 1920. 

 Plates swelling 3,200 per cent when young, increased but 2,000 per cent 

 when nine months old. This total decrease was accompanied by 



