Relation to Deleterious Chemical Agents 441 



From the data presented, it is evident that in defining 

 toxic concentrations it is necessary to speak in terms of the 

 substratum. When soil cultures are employed, the type 

 of soil and amount of organic matter are important. The 

 nutrient solution may modify the action of a poison by 

 forming with it chemical combinations less diffusible or 

 dissociated, and ultimately less injurious. Again, there 

 may be antitoxic action, as in the calcium-magnesium 

 relation. Mass action is also important, as suggested by 

 Dandeno ; thus a seedling injured by 5 cc. of a toxic agent 

 may be killed by a greater quantity of the same concentra- 

 tion. 



266. Method of action. It is not possible at present 

 to state definitely the method of action of all deleterious 

 agents. Many metallic salts and other substances pre- 

 cipitate protein, and it is easy to picture the immediate 

 disturbance of protoplasmic organization effected by such 



