MacDOUGAL— HYDRATION AND GROWTH. 357 



The petioles of some young plants of a Solanmn hybrid in the 

 glass house at Tucson were available on April 21, 1918. Trios of 

 sections were placed in distilled water and acids at 18° and 38° C. 

 witii results as follows : 



18° C. 

 38° C. 



The swelling in distilled water was nearly three times as great 

 at the higher temperature, while in the acid solution a retardation 

 took place which limited the total at the higher temperature to 

 something over a half that possible at the lower point. The total 

 swelling in acid at the lower temperature occupied an hour and at 

 the higher temperature it was a matter of ten or fifteen minutes. A 

 similar speeding up of imbibition in water was observed. The total 

 capacity at the lower temperature was not reached for 8 or 10 

 hours, while at the higher it was something under 2 hours. 



Plants of Phaseolns which formed the experimental material for 

 measuring the growth of pods and seeds bore some pods in which 

 the beans were nearly mature. Pods of the same stage of develop- 

 ment as one which was under the auxograph for recording daily 

 changes were opened and the unripe beans removed. The ends were 

 cut away, the outer coat removed ; the remainder of each coty- 

 ledon made on section of which three were taken from separate 

 pods for swelling. The average thickness was 3.2 to 3.4 mm. and 

 the swellings were as follows : 



Distilled Water. Hundredth Normal Citric Acid. 



( a....l4 % a.... II % 



^° ^ '{ b.... 8 b.... 9.7 



\ a.... 9.6 a.... 6.6 



^ ^ 1 b....ii.7 b.... 4.4 



The higher temperature to which a was subjected appears to be 

 above the point at which maximum absorption or imbibition takes 

 place in distilled water as the swelling was 30 per cent, less than at 

 the point below. The retarding efifect is much more marked in the 

 acid solution, however, as the reduction of the total capacity below 

 that shown at 18° C. amounted to 40 per cent. 



