86 Hydration and Growth. 



was now washed out with water and the sweUing, which had been 

 interrupted in the previous test, was allowed to go on for 147 hours. 

 Swelling was still in progress after 6 days of continuous imbibition, the 

 increase being 1,833 per cent. The total increase up to this time was 

 2,388 per cent. The shrinkage caused by a solution of acidified potas- 

 sium nitrate was very slight, being less than 100 per cent of the origi- 

 nal, and was scarcely more than the effect of the potassium nitrate 

 which was first applied. The original thickness of 0.18 mm. was now 

 reduced to 0.16 mm., much of this loss being attributable to the solu- 

 tion out of some of the water-soluble oat protein and some of the agar 

 (see p. 107). The sections also probably contained some salt and 

 probably a trace of acid. 



The trio of sections were placed under the auxograph in a chamber 

 where the temperature of the distilled water in which they were im- 

 mersed varied between 17° to 20° C. in the 6 days during which the test 

 was carried on. The initial swelling, in contrast with the action of 

 fresh sections, was very slow. Furthermore, the mcrease was contin- 

 ued over a long period, and came to a total of 938 per cent, or less than 

 one-half of the original expansion. 



Sections of plates 0.18 mm. in thickness of agar 90 parts and bean 

 protein 10 parts, to which 0.85 per cent of nutrient salts had been 

 added, were tested in the chamber at 16° to 19° C. The initial treat- 

 ment with distilled water induced a swelling 1,861 per cent in 20 

 hours, during which time the nutrient salts must have been partially 

 dissolved out, so that at the end of this period the liquid was a salt solu- 

 tion in which none of the various components was as concentrated as 

 0.001 M, since about 30 c.c. of water was poured in the dish. The 

 capacity for increase in this solution having been approached, the water 

 (or saline solution) was replaced with a hundredth-normal solution of 

 malic acid, which caused a shrinkage of about 100 per cent in 2 or 3 

 hours. After 7 hours the acid was replaced with distilled water, and a 

 slow swelling ensued. The effects of the alternations here are not sep- 

 arable from those in which the salt is incorporated in the colloid with 

 the first swelling solution. 



A similar set of sections containing nutrient salts were prepared by 

 cutting a trio of strips 7 mm. in length to be placed under the auxo- 

 graph. A free strip 30 mm. long was also placed in the dish. 



The initial immersion in 0.5 per cent nutrient solution was practi- 

 cally complete as to its swelling effects in 18 hours, with an increase of 

 850 per cent. Substitution of hundredth-normal acidified potassium 

 nitrate caused a total additional increase of 75 per cent in 22.5 hours. 

 Replacement of this solution with an alkaline solution of potassium 

 nitrate of the same concentration was followed by a further swelling 

 of 350 per cent in 44 hours. The total swelling of the sections during 

 a period of 110 hours was 1,250 per cent. The concentration of the 



