Dandeno — Relation of Mass Action to Toxicity. ' 457 



with heavy kations ; whereas with stronger solutions and lighter 

 kations, the centers of mass attraction being fewer, and the 

 force consequently greater, the result might be that more light 

 kations would be held by a mere force of attraction. 



Two forces seem to be exerted, one by virtue of the surface 

 exposed (surface tension so-called), and the other by virtue of 

 the mass (gravitation). When the former encounters a substance 

 which is attracted more by surface tension than it is by the 

 mass, then the fine grains will exert a predominating influence 

 upon the solute. When the latter encounters a substance 

 which is more affected by mass than by surface tension, then 

 the coarse grains will exert a predominating influence. At all 

 events, we have the facts derived from the exjDeriments, and it 

 seems but fair to borrow explanations from the physics side of 

 the question. 



In the case of corn seedlings, an aquatic fungus frequently 

 developed if the plants remained in the liquid for a few days. 

 The tendency to curl has also been pointed out. 



An investigation into the cause of the fungus growth showed 

 that, near the root tip, some organic substance exuded from 

 the plant. This substance contained some organic matter 

 which acted, on heating, like sugar. When evaporated on a 

 clean cover-glass, a syrup-like substance remained. For a fur- 

 ther test, seedlings were allowed to send out aerial roots in a 

 moist chamber under a bell-jar, and the root tips were then 

 cut away at a point about 2 nim from the apex. In three hours 

 a drop of clear liquid, about 2 mm in diameter, appeared at the 

 cut end of the root. This drop, upon examination, proved to 

 contain a large proportion of organic matter of a sugary nature, 

 and a small quantity of ash of an alkaline reaction. 



There is no doubt that this substance forms a nutritive 

 material for fungi. Nor is it confined to the root tip, but may 

 be found 20 mm or more from the tip. This was quite apparent 

 in the sand cultures. Upon taking the corn seedlings from 

 the culture media, whether sand or liquid, if the plant had not 

 been killed, the liquid adhering to the tips and elsewhere was 

 of a "glairy" consistency, slightly like white of egg, or like 

 syrup. 



The suggestion is here offered that the reason corn is enabled 

 to withstand stronger solutions of acids and bases than some 

 other seedlings, is in consequence of this secretion. Just what 

 function this might serve is not known. At all events, a great 

 loss to the plant, of organic food, may be suffered, if in cultiva- 

 tion the root-ends be bruised or broken. 



In regard to the curling of the roots, it may be said that 

 chemotropism has something to do with it, but just why it 

 turns this way or that, in a solution where the forces are equally 



