1919] MacDOUGAL, RICHARDS, ^- SPOEHR— SUCCULENCE 413 



The comparisons which may be made upon the basis of such 

 data are almost endless, and a citation of even the salient features 

 of interest cannot be made briefly. The proportionate hydration 

 of the succulent and thin leaves are reversed in acid and alkali. 

 The succulent leaf, which proves to be one-half as acid as the thin 

 leaf, swells most in the alkaline solution; while the thin leaves, 

 with an acidity double that of the thick succulent ones, have an 

 equivalent maximum in hundredth normal citric acid, and take up 

 only half as much water in the alkaline solution, the disproportion 

 between the two expansions being greater than that of the acid 

 alkali ratio in the succulent. 



The thin leaves are characterized by a uniformly high hydration 

 capacity in water in the 3 cases, although reaching a maximum in 

 the salt, a high swelling capacity in acid when fresh, which undergoes 

 a great reduction after drying, while the swelling capacity increases 

 in alkali in parallel treatments. The maximum swelling of the 

 succulent leaves is in water, with great variation in the 3 conditions 

 in which leaves were tested, and with but little variation in the 

 reactions in the salt. The thin leaves, on the other hand, show the 

 maximum and greatest diversity in the salts and more uniformity 

 in water. 



The variations in swelling in the acid solution presented such 

 unusual features that an additional series was planned in which 

 thin and succulent leaves in fresh condition were swelled, then such 

 leaves fully hydrated in water and in various solutions were dried 

 and swelled a second time for comparison with the reactions of 

 leaves dried directly from the living condition. Table IX shows the 

 swellings in o.oi normal citric acid at 15° C. 



The chief departure from the original series is in the matter of 

 the swelling of the fresh succulent leaves, which in this case appear 

 to have been in such a highly hydrated condition as only to be 

 capable of slight expansion. This assumption is in accordance 

 with the fact that after being immersed and then dried they assumed 

 approximately the original thickness on a second swelling. The 

 thin leaves of this series were consistent in their reactions with those 

 previously examined, showing a relatively small expansion from a 

 dried condition. The conditions making possible the greater 

 variations are evidently those recognizable in the succulent type, 



