Water Deficit or Unsatisfied Hydration Capacity. 



99 



was immersed in solutions in a fresh condition, and others were allowed 

 to lie on a window ledge for 24 hours, at the end of which time they 

 were dead, shrunken, but limp, so that they remained in any shape 

 into which they were bent or twisted. The swellings were as follows, 

 on the basis of the original thickness : 



TABLE 78. 



The swelling of the living tissues was greatest and was equal in salt, 

 acidified salt, and hydroxid, while it was low in acid. The dried 

 material swelled most in the salt, while it was least in acidified 

 salt. Increases occurred in all the other solutions, the swelling in 

 alkaline salt being three times as great as hi the living material. 

 It was evidently desirable to measure the water-relations of some 

 simple plant structure which could be brought into the tests with- 

 out anatomical injury and which would not suffer material and 

 immediate injury by submersion. The small tubers of the potato 

 seemed to meet these requirements. 



A number of tubers of the second generation of a hybrid between a 

 domesticated potato and Solarium fendleri of Arizona were available, 

 and as these bodies were in a condition in which they were ready for 

 planting and sprouting, tests were arranged to obtain the swelling 

 measurements in various solutions. Trios of tubers 5 to 8 mm. hi 

 diameter were placed in the dishes after the total and average diameters 

 had been ascertained. The first set swelled 7.5 per cent in 5 days hi 

 distilled water at 14 to 21 C., and the second increased the same 

 proportion in hundredth-normal citric acid in 4 days. A series ar- 

 ranged to obtain the auxographic record as complete as possible was 

 allowed to run for 11 days, at the end of which time the swelling in 

 water amounted to 13 per cent, in hundredth-normal citric and 

 hydrochloric acids 14 per cent, and less than 7 per cent in hydroxid, 

 at temperatures between 14 and 20 C. identical for the lot. Actual 

 shrinkage had not begun in any of the solutions and all solutions were 

 renewed three or four times during the period. 



A set of three with an average diameter of 8.3 mm. was placed in a 

 solution of calcium chloride 3 N acidified to 0.01 N with hydrochloric 

 acid. A steady shrinkage amounting to 3.4 per cent in 4 days began 

 at once. 



