442 



Plant Physiology 



agents, yet it is impracticable to adopt a special grouping 

 based upon a similarity of action within the cell. Among 

 the deleterious agents known, those of economic signifi- 

 cance are of special interest. Of these the important groups 

 are inorganic and organic acids ; caustic alkalies ; salts of 

 the heavy metals ; formalin ; alcohol and anaesthetics ; 



FIG. 126. Indications of the effects of the substratum upon the toxic 

 action of CuSO 4 ; loam (L), sand (S), graphite (G). [Photograph by 

 W. W. Bonus.] 



various organic compounds, including decomposition and 

 hydration products of proteins and lecithins, alkaloids and 

 miscellaneous nitrogenous bodies, also many non-nitroge- 

 nous organic products of diverse composition ; and cer- 

 tain deleterious gases of the carbon series. 



267. Inorganic and organic acids.- -Inorganic acids are 

 usually the most toxic of the acid substances for the higher 



