1917] Forhes: Irrigation Effects of Copper Compounds Upon Crops 463 



Amounts and Significance of Copper in Root Systems 



Of far more and unmistakable importance is the effect of 

 copper on root systems of plants. Under all conditions, whether 

 grown in water culture, in pots, plots, or as field crops, the root 

 systems of plants contain much greater amounts of copper than 

 do the aerial portions, as is shown briefly in the following con- 

 densation of results : 



TABLE XXXI 



Summary of Copper Content of Tops and Roots op Plants 



No. of 

 samples 



Corn, beans, and squash in water cul- 

 tures, poisoned but living 3 



Ditto — killed by copper 3 



Corn grown in soil containing .01 per 



cent of Cu as Cu(OH)3CuC03 1 6.50 152.00 1 to 23 



Corn grown in soil containing .025 per 



cent Cu as Cu(0H),.CuC03 1 21.00 728.00 1 to 35 



Corn grown in soil containing .05 per 



cent Cu as Cu^S 1 12.50 171.00 1 to 14 



Bean series grown in soils containing 



Cu as pptd. carbonate .0025 to 1.5 



per cent Cu in soil -.. 9 26.00 1431.00 1 to 55 



Corn series grown in soils containing 



Cu as CuoS .01 to 1 per cent Cu 



in soil 7 51.00 702.00 1 to 14 



Corn series grown in soils containing 



Cu as chrysocolla, .05 to 1 per cent 



Cu in soil 3 13.00 266.00 1 to 20 



Corn series grown in soils containing 



Cu as pptd. carbonate, .0025 to .05 



per cent Cu in soil 4 13.00 416.00 1 to 32 



Excluding samples grown in water cultures, the roots of 

 which were cleaned with 4 per cent HCl, probably wdth loss of 

 some copper, the root systems of experimental cultures contained 

 averages of from fourteen to fifty-five times as much copper as 

 the aerial portions of the plants. Furthermore, fine roots of corn 

 were found in one instance to contain about three times as much 

 copper as coarse roots of the same sample, and, finally, the 

 maximum amount of copper, as determined both by analysis and 

 by observation, in water cultures, was found in the root tips 



