446 



Plant Physiology 



dicated under the discussion of lime, that many plants 

 thrive under basic conditions, while others yield best when 

 the substratum is acid. 



269. Salts of the heavy metals. The salts of the 

 heavy metals constitute a group of the most toxic agents 

 known. The various soluble inorganic salts of the same 

 metal are commonly of about equal toxic value. The 

 table given below is comparable to that given for inorganic 

 acids, the concentrations representing those which kill the 

 majority of the roots in 24 hours :- 



Kanda employed pots holding two liters of soils in some 

 experiments with horse beans. These were in one case 

 watered daily with copper sulfate to such extent that at the 

 end of three weeks the pot contained 26.394 grams of the 

 salt. This amount caused onlv a slight reduction of root 



*> CJ 



growth, but stem growth was greater than in the control. 

 Copper compounds are extremely injurious to certain 



