88 Hydration and Growth. 



Another test was made for the purpose of comparison of the effects 

 of the swamp water with those of a solution of nutrient salts in which 

 the initial swelling in the nutrient solution was 861 per cent in 20 

 hours, which was less than in swamp water. A solution of acidified 

 potassium nitrate was substituted and a swelling of 55 per cent ensued 

 in 55 hours. Replacement of the acidified salt solution by distilled 

 water was followed by a long-continued swelling which increased the 

 volume 111 per cent in 40 hours. The total increase of this section 

 was thus 1,027 per cent, as compared with 1,333 per cent in bog 

 water alone. 



The obvious importance of these reactions is amply illustrated by 

 the changes in environmental conditions to which many aquatic plants 

 are subjected in the course of a season or even in a day. 



Growth in all probability implies the incorporation of new material 

 in the colloid which adds to the hydration total of the mass. It is not 

 easy to arrange the introduction of unhydrated particles in a swelling 

 mass, but it was deemed worth while to bring a desiccated trio of sec- 

 tions into swelling under a similar trio which had already undergone 

 some expansion. 



Three sections of an agar 90, peptone 10 parts, 0.18 mm. in thick- 

 ness, were swelled in distilled water until an expansion of 1,195 per 

 cent had been reached in 4 hours ; a second series of sections were gently 

 slid under the first lot, the pen was readjusted to register continuously, 

 and a fresh lot of water was added (fig. 14). 



9am m^;; iZp.m 



Fig. 14. 

 Course of swelling of a 

 double trio of sections 

 of agar and peptone, 

 the second being added 

 after the first was par- 

 tially hydrated. See 

 text, page 88. 



A swelling of the two trios now followed which reached satisfaction 

 in about 14 hours, which amounted to 708 per cent, calculated on the 

 thickness of both. Most of this swelling, however, was in the freshly 

 added sections, in which the swelling was 1,083 per cent in 4 hours, 

 and a lesser amount was due of course to the original trio. The final 

 total of the pair of trios swelled only 1,153 per cent, while the first set 

 had increased 1,195 per cent before the second pair was added and had 

 not yet completed its swelling. It seems fair to infer that increase 

 of thickness diminishes the proportionate increase. 



A second test was made in which the swelling of the first trio reached 

 about 800 per cent in 2 hours and then a fresh section was thrust under 



