74 Hydration and Growth. 



nitrate solution was followed by a very slight swelling. When this 

 solution was replaced by swamp water an increase of 333 per cent 

 followed in 40 hours. The two tests were parallel, except that the 

 initial treatment in one case was with nutrient solution in which the 

 salts were more concentrated than in the swamp water used in the 

 other. The final swelling in the second case is greater and may be 

 attributed to the initial salt action. 



In a partial repetition of the above test, the sections placed in culture 

 solution swelled 861 per cent in 20 hours. Lengthening the immersion 

 in acidified potassium nitrate to 55 hours was accompanied by a 

 swelling of 55 per cent. Replacement with distilled water set up a slow 

 increase which resulted in a gain of 111 per cent in thickness in 40 

 hours. The total increase was 1,027 per cent, while the one finished 

 in swamp water swelled 1,388 per cent. 



The relative effects of swamp and bog water on biocolloids were 

 tested in still another way. Plates of agar-oat protein were prepared 

 in which strips of webbing of cotton were embedded in the soft material 

 as it cooled for the purpose of testing the influence of certain purely 

 mechanical features on swelling. Portions of the plates dried down to 

 a thickness of 0.18 mm. in the clear portion of the plate and sections 

 from this swelled 2,111 per cent in bog water and 1,195 per cent in 

 swamp water at 15° C. Sections containing webbing were 0.58 mm. 

 in thickness and the actual increase of such sections was 491 per cent 

 in bog water and distilled water and 371 per cent in swamp water. 

 If the increase be calculated on the assumption that the webbed sec- 

 tions included as much biocolloid as the free sections, the proportions 

 would be 1,583 per cent in bog water and distilled water and 1,195 

 per cent in swamp water. 



Swamp water has been found to affect absorption and swelling in the 

 same manner as an equivalent solution of calcium sulphate. Swelling 

 and absorption is retarded by swamp water in salted biocolloids and 

 in sections of plants containing a large proportion of pentosans and a 

 low protein-content. Biocolloids with a high protein and salt content, 

 on the other hand, show an enhanced absorption in swamp water. 

 Inferentially, plants of similar constitution would carry on absorption 

 readily and thrive in swamp waters. Whether adaptation to swamp 

 habitats actually takes this course is not known. 



An extension of these measurements was made to ascertain the 

 effects of water and soil solutions which were in common use at the 

 Desert Laboratory upon a biocolloid, a mixture consisting of 6 parts 

 of agar, 2 parts of mucilage of Opuntia, 1 part of gelatine, and 1 part 

 of bean protein. This had been poured in the usual manner and dried 

 to a thickness of 0.2 mm. Sections of the usual size were placed in 

 dishes imder the auxograph. Distilled water of the grade used in 

 making up all of the solutions caused a swelUng of 1,750 per cent; rain 



