358 MacDOUGAL— HYDRATION AND GROWTH. 



The material in series b taken at a later date and with seeds 

 which seemed to be more nearly mature, showed an increase in 

 swelling in distilled water of about 45 per cent, over the total at the 

 lower temperature, while the swelling in acid was less than half 

 that at 18° C. The average of the two series is such that the swell- 

 ing in distilled water is nearly the same at both temperatures, while 

 in acid the average at 18° C. is 10.4 per cent., which is nearly double 

 that at 38° C. at which point the hydration capacity seems to be in- 

 variably lower than at the lower temperature. These averages rep- 

 resent a total of six cotyledons each. 



A final test of variations in temperature upon material in an 

 acidified condition was made with dried sections of Opuntia. These 

 sections 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 was 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 thickness 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 dis- 

 tilled water, as will be apparent from the following measurements 

 obtained from sections which were .43 to .46 mm. in thickness. 



Swelling in 

 Distilled Hundredth Normal 



Water. Citric Acid. 



18° c 315% 360% 



385 430 



486 460 



Average 395% 417% 



28° C 453 460 



38° C 500 477 



413 400 



Average 457 439 



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 influ- 

 ence which the condition in question may exert on the rate of 

 growth is obvious. Thus the course of enlargement of an organ or 



