Hydration and Growth of Colloids and Cell-masses. 



123 



A final test of variations in temperature upon material in an acidi- 

 fied condition was made with dried sections of Opuntia. These sec- 

 tions were made by slicing away the chlorophyllous layer from one 

 side of the flat joint and drying the remainder in the desiccator and in 

 sheets of blotting-paper in such manner that buckling and crumpling 

 were prevented. After all of these precautions were taken, however, 

 the measurement of the sections was subject to some error, due to the 

 fact that the fibrovascular strands remaining would increase the thick- 

 ness under the calipers without reacting in due proportion to the action 

 of the swelling agent. A wide range of figures was obtained, but it 

 was apparent that a rise in temperature did not have an effect on 

 material in acid equivalent to that in distilled water, as will be apparent 

 from the measurements obtained from sections which were 0.43 to 

 0.46 mm. in thickness (table 100). 



Table 100. 



The increase in swelling in distilled water is seen to be about twice 

 that in the acid in the rise from 18° C. to 38° C. The influence which 

 the condition in question may exert on the rate of growth is obvious. 

 Thus the course of enlargement of an organ or of a cell-mass, in so 

 far as this consists in hydration, may vary widely in the first instance, 

 because of the residual acids in the colloids, and the balance or accumu- 

 lation of this will in turn depend upon the effect of the enzymic or 

 respiratory processes in metabolism. It is obvious that a rise of 10 

 degrees from the customary morning temperature of 15° C, which has 

 accompanied so many of these experiments, might result in an ac- 

 celeration of growth determined by the reduced acidosis of the plant. 

 A rise from the same temperature later in the day or under other con- 

 ditions of illumination would necessarily have a different, result. An 

 extension of the attempts to bring rates of growth into a figure or 

 formula, therefore, would be a forced application of knowledge of one 

 process to a complicated procedure which results in no positive advance. 

 Variation of temperature results in modification of the rate of enzymic 

 processes and of the forms of metabolism included under and associated 

 with respiration, in modification of the rate of absorption of water by the 

 organism from its medium or substratum, and modification of the water- 

 holding capacity of the cell-colloids after a mode determined by their 

 carbohydrate-protein ratio and by their state of acidosis. The actual 

 increase in volume, will also be influenced to some extent by the continual 

 water-loss from the surface. 



