Effect of Copper Compounds 17 



paper (1896) in which he brings most interesting facts to light. The 

 quantity of copper in any species of plant varies with the individuals of 

 that species, even when grown on the same soil, in the same year, and 

 under similar conditions. The copper content of certain plants is put 

 forward as a table, the years 1894 and 1895 being compared, and 

 enormous differences are to be noticed in some cases. A quotation 

 of the table will illustrate this more clearly than any amount of 

 explanation. 



Milligrams of copper in I kilog. dry matter. 



1894 1895 



min. max. 



200 680 



190 230 



10 30 



10 70 



40 200 



150 160 



110 150 



110 150 



60 110 



70 80 



70 290 



60 70 



Paprika pods 790 1350 230 400 



II. EFFECT OF COPPER ON THE GROWTH OF HIGHER PLANTS. 



1. Toxic effect. 



(a) Toxic action of copper compounds alone in water cultures. 



The method of water cultures has been largely applied to determine 

 the relation of copper compounds to plants. Twenty years ago (1893) 

 Otto discovered the extreme sensitiveness of plants to this poison when 

 grown under such conditions, as he found that growth was very soon 

 checked in ordinary distilled water which on analysis proved to contain 

 minute traces of copper. Controls grown in tap water gave far better 

 plants, but this superiority was attributed partly to the minute traces 

 of mineral salts in the tap water, and not only to the absence of the 

 copper which occurred in the distilled water. 



Tests made at Rothamsted have carried this point still further. 

 Pisum sativum, Phaseolus vulgaris, Triticum vulgare, Zea japonica, 

 Tropeolum Lobbianum, sweet pea (American Queen), nasturtium, and 



B. 2 



