414 



BOTANICAL GAZETTE 



[may 



not the least important feature being the greatly enlarged paren- 

 chymatous cells. It is to be seen that immersion and drying, and 

 also simple drying, reduce the swelling capacity of thin leaves in 

 acid, but no such decrease occurs in the succulent leaf. 



The principal changes which take place in swelling consist in 

 the extraction of acids and acid salts, as indicated on the previous 

 pages, and of the hexoses as yet undetermined. Any mucilages or 

 pentosans present would of course diffuse at a rate so slow as to be 

 of no consequence in the present experiments, 



TABLE IX 



Material 



Fresh leaves 



Above leaves dried and rehy- 

 hydrated* 



Fresh dried leaves* 



Thin 



Thickness 



mm. 

 / 0.4 

 \ 0.41 



/ 0.23 

 \ 0.25 



(0.38) 

 O. 2 



(0.38) 

 0.2 



Swelling 



Percentage 

 125 

 184 



42 

 20 



25 

 62 



Succulent 



Thickness 



mm. 

 1-4 

 1-4 



0.5-0.6 

 0.63 



(1.2) 



0.5 

 (l.i) 



0.38 



Swelling 



Percentage 

 21 



25 



95 

 91 



120 

 92 



* Expansion in terms of dried thickness. 



The swelling of fresh leaves of both types in water reaches the 

 limit in less than 2 hours, the rate of extraction of acid in the 2 

 types of leaves being equivalent, and the proportionate expansions 

 not widely different. When such leaves are dried the thin leaves 

 attain the limit in water inside of 2 hours, while the succulent 

 leaves continue to expand for 6 hours with an escape of acid about 

 half that from the thin leaf during the same time. 



If attention be turned to the reactions in acids, it is seen that 

 thin leaves swell more than succulents in such solutions when fresh, 

 and that the swelling extends over a greater length of time, while 

 the total swelling in a dried condition is accomplished in a few 

 minutes. The succulent leaves, on the other hand, require a period 

 of as much as 6 hours to reach full hydration from a dried condition. 



While the effect of the residual acidity is discernible in some of 

 these relations, it is evident that this factor is not the dominating 



