Water Deficit or Unsatisfied Hydration Capacity. 



97 





TABLE 74. 



p. ct. 



Distilled water 7 



Citric acid, 0.01 N 4 



Sodium hydroxid, 0.01 M 6.2 



Potassium chloride, hydrochloric acid, 0.01 M. Immediate and marked shrinkage. 



The rapid and immediate shrinkage of these thin sections in the 

 acidified salt solution was so striking that a second measurement was 

 made, in which thicker sections swelled 4.4 per cent in the acidified 

 salt solution within a few minutes and then began to shrink to the 

 original dimensions and to smaller volume. Imbibition in the salt solu- 

 tion alone showed two phases : first, a very rapid swelling to a volume 

 near the maximum capacity, then a slow increase which was still hi 

 progress 24 hours later and which at that time had brought the section 

 to a thickness 10 per cent greater than the original. Such material in 

 acids swells quickly and more gradually than in the combined solu- 

 tion, then slowly shrinks to the original dimensions and below. The 

 presence of the salt accentuates the action of the acid, as it did also in 

 the swelling of stems of Verbena in similar solutions, the increase in the 

 acid being but 2.8 per cent, while it was 4 per cent in the combined solu- 

 tion, the explanation of which is probably to be sought in the com- 

 bined effects of acids and bases (fig. 18). 



6am 9 10 



10 H I2p.m lam. 2 



i 1 r 1 r~ 



d. 



FIG. 18. Swelling of tangential slices from tips of asparagus shoots at 14 to 17 C., X 20, on 

 scale ruled to 5 mm. and 1-hour intervals, a, swelling of trio 3.8 mm. in thickness 7 per 

 cent in water; b, swelling of trio 3.7 mm. in thickness 4 per cent in hundredth-normal citric 

 acid; complete within a few minutes, followed by gradual shrinkage; c, swelling of trio of 

 sections 6.2 per cent in sodium hydroxid with final shrinkage; d, slight swelling of trio of 

 sections in hundredth-normal potassium chloride and hydrochloric acid and then rapid 

 shrinkage. 



Other aspects of the matter of permeability and swelling are offered 

 by the reactions of young bean seeds which had not attained more than 

 an eighth of their final volume and had a diameter of 2.8 mm. These 

 were tested hi a series parallel to the above and swelled as follows: 



TABLE 75. 



p. ct. 



Distilled water 8.2 



Potassium nitrate, 0.01 M 9-9 



Potassium nitrate, citric acid, 0.01 N 8.2 



Citric acid, 0.01 N 5.4 



Potassium hydroxid, 0.01 M 12.5 



The proportions here were also those of an agar-albumin mixture, 

 but the high swelling in the acidified salt was not shown. The beans 



