416 Vniversily of California Publications in Agricultural Sciences [Vol. 1 



Cu Cu 



in tops in roots 

 Culture Condition p. p.m. p. p.m. Ratio 



Copper carbonate, 0.01% Cu Leaves faintly striped 



(precipitated) normal weight 6.50 152.00 1:23 



Copper carbonate, 0.025%. Cu Leaves strongly striped 



(precipitated) three-fourths yellow, 



half weight 21.00 728.00 1:34 



Copper sulphide, 0.05% Cu Faintly striped leaves, 



normal weight 12.50 171.00 1:18 



In this table a general relation is shown between the toxic 

 effects in the aerial portions of the plant, and the amounts of 

 copper in root systems ; but as to the soils employed toxic effects 

 are influenced both by amounts and character of copper com- 

 pounds present, as is shown further on following pages. 



In view of the fact that the small increase of copper in the 

 carbonate cultures, from 0.01 to 0.025 per cent, caused severe 

 toxic effects attended by an increase of copper in root systems 

 from 152 to 728 p. p.m. of dry matter, it seemed desirable to in- 

 vestigate thoroughly the quantitative relations between the copper 

 in roots and the toxic effects as show^n in vegetative grow^th. It 

 was expected in this way to find a means of determining whether 

 a plant contained an injurious or killing dose of copper, just as, 

 analogously, killing doses of poisons in animals may be ascer- 

 tained. With this end in view cultures of corn, beans, and 

 squashes were grown in water, in pots of soil and in garden 

 plots; and roots and top portions were examined quantitatively 

 for copper. 



In preparing samples of roots for analysis, washing with 

 4 per cent hydrochloric acid w-as carried out with water cultures, 

 but most of the samples were prepared by washing with large 

 quantities of copper-free water saturated with carbon dioxide, 

 until the washings showed no trace of copper. By still a third 

 method the soil adhering to a sample was analyzed for copper, 

 the ash was then determined and assumed to be soil, and a cor- 

 responding amount of copper subtracted from the total found. 

 For details see "Methods of Analysis." All of these methods 

 undoubtedly give conservative figures for copper in root systems 

 inasmuch as solvents not only remove externally adhering com- 

 pounds but may also gradually act upon the copper content of 



