50 Hydration and Growth. 



The measurements in table 43 were taken at the end of 30 hours, 

 at which time expansion was not complete, although further swelling 

 would not materially alter the relative values. The proportion of 

 salts actually present was about one-twelfth of the biocoUoid, which in 

 volume amounted to about 12 c. mm. The dishes held 30 c. c, and 

 from these data it may be possible to calculate proportions of salts 

 and acids for comparison with the cases in which- the salts are applied 

 in solution. 



A second test was made with the same biocoUoid as above, but to 

 which had been added but one-tenth of the foregoing proportion of 

 culture salts. The plates were thinner, but the swellings were made 

 at the same temperatures and under approximately the same con- 

 ditions, with results as follows: 



Table 44. 



p. ct. 



Distilled water 1,667 



Citric acid, 0.05 N 667 



Citric acid, 0.005 N 899 



Citric acid, 0.0005 N 1, 139 



Citric acid, 0.00005 N 1,500 



The swelling of these plates, which were 0.18 mm. in thickness, was 

 carried out at a temperature of 16° to 17° C, and the expansion in 

 distilled water shows the retarding effect of the salt alone when com- 

 parison is made with agar-bean protein mixtures not treated with the 

 nutrient solution. The citric acid in its heaviest concentration is 

 equivalent to the strongest solution encountered in plants in this work, 

 at which it is seen to retard swelling very much. Reduction of the con- 

 centration of the salts seems to be followed by a proportionate increase 

 of water-capacity, in a fairly regular manner. The discrepancy in the 

 swelling in 0.005 N acid in the more heavily salted plates is probably 

 an instrumental error and will be so considered until confirmed. In 

 the most attenuated solution of acid the swelling approaches that of 

 distilled water, in which the salt effect alone is apparent. 



The series of increases of a biocoUoid given on page 48 present the 

 general differences and relations of sections from plants, and these, 

 rather than the one in table 44, which has such a high swelling coeffi- 

 cient in water, are of the character more usually encountered in cell- 

 masses. It is to be recalled, however, that the composition of the 

 biocoUoid, including a mucilage, albumin, and amino-acids, is one 

 which may well be duphcated in the plant, and it may be the recurrence 

 of such combinations which would furnish the phenomena so prominent 

 in the involutions of the cell. 



The principal deductions of the present work support the conclusion 

 that agencies or conditions which increase the hydration capacity of 

 protoplasm accelerate growth, and any factor which tends to lessen 

 either the rate of absorption or the total hydration capacity of living 



