98 Hydration and Growth. 



were intact, with an unbroken coat. It was probable, therefore, that 

 osmosis may have played some part in the absorption in water and the 

 solutions. 



A second lot of the growing beans, which had an average diameter 

 of 2.4 mm., was allowed to desiccate for 3 days, and when they had 

 become hard and dry and were dead, the swelling tests were made 

 with them, yielding the f ollowing results : 



TABLE 76. 



p. ct. 



Distilled water 29 . 2 



Potassium nitrate, 0.01 M 22 . 9 



Potassium nitrate, citric acid, 0.01 N 32 . 5 



Citric acid, 0.01 N 29 . 2 



Potassium nitrate, potassium hydroxid, 0.01 M 31 .3 



Potassium hydroxid, 0.01 M 15.8 



It is evident that the activity of the vacuole is not the determining 

 or dominating factor in the water-deficit or unsatisfied hydration 

 capacity; if it were, the greatest swelling would have taken place in 

 water. The action of the salt was not increased by the addition of 

 acid in the swelling of the living cells, but such an effect was produced 

 in the dried beans. The interferences were much less in the dried 

 material, the swelling in acid being but little short of that in water, 

 while it was relatively much less in the living material. 



Young leaves of Abronia latifolia which had been allowed to wilt for 

 two days while attached to stems in a ventilated room were cut into 

 suitable strips free from the midrib and the larger veins in preparation 

 for swelling tests. The spongy texture made it impossible to measure 

 thickness with accuracy, but this was estimated as 1 mm. Increases 

 in thickness were measured, as follows: 



TABLE 77. 



p. ct. 



Distilled water 40 



Potassium nitrate, 0.01 M 80 



Potassium nitrate, citric acid, 0.01 M 55 



Citric acid, 0.01 N 50 



Potassium nitrate, potassium hydroxid, 0.01 M 50 



Potassium hydroxid, 0.01 M 60 



Potassium nitrate gave a maximum swelling, a lesser one when acid 

 was added with the salt, and still less swelling ensued when acid alone 

 was used. The swelling in distilled water probably represents a nor- 

 mal imbibition total under the undisturbed conditions in the leaf. 

 The partial neutralization of the acid by the addition of hydroxid 

 gave a swelling determined by the acidified salts formed. 



Half -grown succulent leaves of Cakile sp. were taken from the beach 

 at Carmel, August 23, 1917. The total acidity, as determined by Pro- 

 fessor H. M. Richards, was found to be equivalent to 0.30 c.c. hun- 

 dredth-normal sodium hydroxid per gram of fresh material. The 

 strips of leaf-blades, which were cut in such manner as not to include 

 any of the main veins, had an average thickness of 1.2 mm. One lot 



