398 BOTANICAL GAZETTE [may 



present; for upon further addition of adsorbents the minimum at the 

 end of the fifteenth day is succeeded by a higher rate of transpiration. 

 Filters of finer grain are more beneficial, while the adsorptive power of 

 humus is very much higher than that of any of the crystalline substances 

 used. The optimum and maximum rates of transpiration occur on 

 the fifteenth and twentieth day and lie near together. Reference 

 to the total amount transpired shows that the adsorption of car- 

 borundum and humus is about three to four times greater than that 

 of quartz. The transpiration data serve excellently as a basis for 

 assigning a limit to the magnitude of the toxic effect, and as an 



o o 



expression of the amount of the unknown body adsorbed both in 

 terms of the total adsorption, and as a percentage of the surface factor 

 of grains. The results with CaC0 3 also show that the plants are not 

 affected by conditions of acidity or alkalinity, and that growth seems 

 to be more materially affected by the specific action of the organic 

 toxins present. Whatever the nature of the filter used, that the 

 increased tolerance of wheat seedlings to bog water is actually due to 

 the adsorptive power of the filters is sustained by the fact that the 

 decrease of the poisonous effects of bog water is apparently a function 

 of surface of particles and is approximately proportionate to the 

 quantity of the solid body used. The solution, decidedly toxic without 

 the solid, becomes capable of supporting a more than normal growth. 



The outcome of these preliminary tests is, therefore, that the con- 

 ditions giving rise to decreased physiological activity, to xerophily, 

 and to zonation of bog plants are not found in the depletion or increase 

 of mineral nutrients in bog water, nor in a low soil temperature, but 

 lie rather in the toxicity of the soil substratum, i. e., in the production 

 of unfavorable soil conditions brought about by the plants them- 

 selves. ■ • 



However, experiments by the water-culture method may not always 

 be serviceable as a safe basis for argument concerning soil conditions. 

 A number of life relations of the plant in a water culture become 

 changed when in the soil. In what particular manner the toxic 

 bodies are held by the adsorptive force of the filters is not clear 

 judged by physical or chemical analysis. The marked retentl ° n n ° a 

 the toxins of bog water observed may be due to causes other t an 

 direct condensation on the surface. No experiments were ma e 



