lOO BOTANICAL GAZETTE [febrtjary 



small amount of toxic agent enabled the plants to work more economi- 

 cally with a given amount of nutritive material. It is possible, when 

 toxic agents are present in small amounts, that they excite th^ cells 

 to greater activity, as a result of which the cells are able to utilize 

 more fully the materials at their disposal, or to overcome retard- 

 ing conditions of their environment. Such an action would be 

 analogous to the "activating" influence of certain inorganic salts upon 



enzymes 



stimulating agents may 



matter 



plant or of the cell. The writers have shown (:07a, :076) that 

 deleterious waste products are excreted from living plants, and that 

 the accumulation of these substances may be detrimental to vegetable 

 growth unless some agency removes or destroys the excretory prod- 

 ucts, either by the formation of harmless compounds, or more simply 

 by precipitating them. It is well known that salts of the hca\y 

 metals, which in small amounts exert a stimulating action on plants, 

 will also bring about a precipitation of proteid-like bodies. When 

 larger amounts are present, these substances not only combine with 

 the excreted proteid bodies at the surface of the plant, but also 

 exert this same action on the living protoplasm within the plant^ 

 causing death. 



If the excretory products mentioned be of the nature of proteids, 

 it is easy to see how beneficial conditions might arise by the continual 

 precipitation of the harmful excretions. In other cases it is possible 

 that the compounds which exert a stimulating action may set up 

 chemical processes which, while not precipitating excretions, never- 



theless render diem harmless to the plants which produce them. 



small 



[uantities of toxic ag 



products, and the maintenance of a sanitary environment for the 

 growing plant. It is not at all improbable that each of the processes 

 mentioned may act as factors in increasing plant growth at different 

 times and under different conditions. 



The oxidizing power of the plant roots was sho^-n in several 



msfences by the formation of colored compounds which stained the 

 root? . 



