6 Introduction 



endosmosis absorbs whatever is presented to its external surfaces, so 

 that whenever abnormal substances are taken up by a living plant it is 

 in consequence of some interference with the vital functions of the roots 

 caused in the first instance by the deleterious influence of the agent 

 employed. 



In spite of the enormous amount of work that has been done on 

 this subject of toxic action and stimulation it is yet too early to discuss 

 the matter in any real detail. A voluminous literature has arisen 

 around the subject, and in the present discussion some selection has 

 been made with a view to presenting ascertained facts as succinctly as 

 possible. No attempt has been made to notice all the papers ; many 

 have been omitted perforce ; it would have been impossible to deal 

 with the matter within reasonable length otherwise. A full and 

 complete account would have demanded a ponderous treatise. This 

 widespread interest on the part of investigators is fully justified, as the 

 problems under discussion are not only of the highest possible interest 

 to the plant physiologist, but hold out considerable promise for the 

 practical agriculturist. 



