Fluctuating or Alternating Hydration Effects, 87 



salts was reduced during one period of 23.5 hours and during the re- 

 mainder of the time the concentration ^was about a hundredth molar 

 at a temperature of 18 to 21 C. No appreciable change in length of 

 the tested trio of sections or of the free long strip occurred (see p. 19). 



The effects of swamp water, which has already been shown to retard 

 hydration, were tested in this connection. The first lot of water of this 

 kind was procured from the sedge-grass swamps near Anoka, Minnesota. 

 Sections of agar 90 and oat protein 10 parts, which were 0.18 mm. 

 in thickness, were swelled in this at 17 to 19 C. Imbibition was 

 rapid during the first 12 hours, during which time a total enlargement 

 of 972 per cent took place. At the end of this time the rate had 

 decreased notably, but was maintained in such manner that in 4 days 

 an additional swelling of 361 per cent was recorded. The volume 

 was now practically stationary and the test was closed at the end of 

 108 hours. This long-continued swelling at a low rate and low total 

 was in contrast with swellings of similar sections in distilled water and 

 in nutritive salts. 



The trio of sections placed in distilled water at the same time as the 

 above swelled 2,361 per cent in 3 days, and as increase had ceased, the 

 distilled water was replaced with swamp water, with the result that a 

 slow shrinkage ensued, which, however, amounted to only 36 per cent 

 of the original volume in 2 days. 



It was next thought important to test the swelling of sections con- 

 taining salts in swamp water, and a mixture of agar 90 parts, bean 

 protein 10 parts, and nutrient salts 0.85, 0.18 mm. in thickness, was 

 swelled at the temperatures ofl7tol9C. The initial swelling was prac- 

 tically complete in 16 hours, at which tune an increase of 1,082 per 

 cent had taken place. Replacement with acidified potassium nitrate, 

 hundredth normal, for 36 hours caused no appreciable change in vol- 

 ume, but when this solution was washed away in swamp water, swell- 

 ing was resumed and a further increase occurred, most of which took 

 place in the first 4 hours, but which was still in progress at a very slow 

 rate at the end of 38 hours. The enlargement in the swamp water 

 during this final period was 306 per cent, the total swelling being 

 1,388 per cent. 



Sections identical with the above were first placed in a 0.5 per cent 

 nutrient solution, in which a swelling of 888 per cent occurred in 

 17 hours, at which time the pen of the auxograph was tracing a hori- 

 zontal line. Replacement with acidified potassium nitrate produced 

 no effect beyond a very slight swelling. When the acid solution was 

 washed away with the swamp water swelling began and an increase 

 amounting to 333 per cent followed in 40 hours. This final action was 

 fairly equivalent to that of the preceding series, except that the sub- 

 stitution of swamp water for the acidified salt was followed by a much 

 slower but more extended rate of initial swelling. 



