140 BOTANICAL GAZETTE [AUGUST 
presence of these substances in small amounts, and the behavior 
of the plants is very much like those grown in a 0.ooo1 per cent. 
solution of strychnin or atropin sulfate. 
The striking agreement of results obtained from such a variety 
of material seems sufficient proof that the factors inhibiting plant 
growth and plant association and succession are at least in part 
due to the plants themselves. Carbon black and calcium carbonate 
add no soluble matter to the solutions (2), hence it becomes certain 
Fic. 5.—Average plants of Phaseolus multiflorus, showing effect of bog water 
variously treated. Numbers as in the text, p. 133. 
that the beneficial effects cannot be due to the introduction of 
nutrient material but to the taking up, i. e., the adsorption of injurious 
substances present. This would indicate, therefore, that the chang® 
in the soil conditions are produced by noxious substances formed 10 
the absence of O,. They may be products of decomposition, per 
haps they are in part plant excreta, but whatever their nature, they 
are water-soluble toxic bodies which retard oxidation in the tiss¥® 
and decrease transpiration, thus causing xerophily, stunting, and 
even death, 
It may be readily questioned whether part of the response 
from a deficiency of oxygen in the soil. The evidence obtain 
arises 
ed by 
