Hydration and Growth of Colloids and Cell-masses. 121 



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 stances would have such effect that the hydration of the sections would 

 not result in the exact resumption of the former condition of the cell- 

 colloids. The field of action of the colloid within the limits mentioned 

 offers a most promising group of phenomena, the study of which may 

 be expected to contribute in an important manner to knowledge of the 

 mechanics of protoplasm. 



Adequate parallel measurements of the effects of temperature on 

 growth of Opuntia were not made, but some records are available 

 which show the variation caused by the rise upon material grown at 

 the lower temperature in the above etiolated series. Elongation by 

 growth of the stems in question was at the rate of 5.2 mm. daily at 

 16° to 18° C. and 11 to 17 mm. daily at 30° to 32° C. The increase 

 amounted practically to a doubling for a rise of 10° C. The swelling 

 in transverse sections of similar material was 4.9 per cent at 17° to 

 19° C. and 7.5 per cent at 30° to 31° C. in distilled water; and 4.9 per 

 cent at the lower temperature in acidified potassium nitrate and 9.5 

 per cent at the higher temperature. The increase by swelUng trans- 

 versely was therefore slightly less than double, with a fair inference that 

 it would have been greater in the axis of elongation or growth. It is 

 to be seen, therefore, that in the elongation of the vegetative axes of 

 plants the temperature effect is a complex one, and that the accel- 

 erating effect of rising temperature may be primarily an increase 

 in absorption capacity by altered metabolism, including lessened 

 accumulations of acids. 



An illustration of the failure of rising temperatures to increase 

 hydration and swelling under some conditions is furnished by the 

 behavior of sections of joints of Opuntia taken in a condition of acidosis 

 in the morning. These increased no more at 27° C. than at 20° C. 

 (see p. 119). The' experiences with biocoUoids must be drawn upon 

 with care when a parallel is sought. The sections of a biocolloid 

 containing the mucilage from Opuntia and bean protein were seen to 

 swell 2,400 per cent at 22° C, while the swelling was less than 1,800 

 per cent at a temperature 5 degrees higher, but the lower figure in this 

 case was probably due to the fact that the plates of colloidal material 

 began to break up and dissolve out • at a lower stage of hydration, 

 thus ending the record. 



Various tests of material were made for the purpose of ascertaining 

 the conditions prevailing among plants of different types. In mid- 

 April, sections were taken from the terminal elongation internodes 

 of Phoradendron growing near the Desert Laboratory, parasitic on 

 Parkinsonia microphylla. Such sections were about 3 mm. in length 

 and half that thickness. Swelling was 3 and 5 per cent in distilled 

 water at 20° and 30° C, respectively, but no appreciable difference 

 could be detected between the increases in hundredth-nomal citric acid 

 at the two temperatures. 



