Copper in plants 



D. T. MacDougal 



The recent note by Dr. R. M. Harper in Torreya, No- 

 vember-December 1935, dealing with copper in plants, impels 

 me to recall a note by myself on this topic in the Botanical 

 Gazette, January 1899, page 69. This note was descriptive of 

 the presence of copper in the wood of a tree of Quercus macro- 

 carpa which had been submitted to the Department of Chemis- 

 try of the University of Minnesota for analysis. The metal was 

 found "in the form of finely divided, reddish brown particles in 

 the tracheides, vessels, and medullary parenchyma." This de- 

 posit was marked in about ten of the annual rings and in a quan- 

 tity amounting to 500 mg. to each kilo of dry wood, of which it 

 thus formed a proportion by weight of 0.5 per cent. 



Although no investigation was made of the soil in which the 

 tree grew it was assumed that the metal was absorbed from 

 float copper from the formations in the Lake Superior region. 

 While at the time the examination was made it was assumed 

 that the tree had been absorbing copper for a decade it is now 

 known that the ascending sap in the oaks may occupy many 

 layers at one time. The tree may have therefore taken up all the 

 copper found in one year. Whether its death was the result of 

 such absorption was not known. 



My own studies in movements of sap in plants throws no 

 light on the mechanism by which this metal was found to be 

 chiefly concentrated in the bark of several plants including the 

 willow, as cited by Harper. No case of actual excretion from the 

 sap conducting layers out through- the cambium is known and 

 the presence of a high proportion of metal in the bark conse- 

 quently presents an interesting puzzle. 



At the time of the preparation of my original note I had 

 access only to the paper by Skertchly, mentioned by Harper, 

 and to one by Lehman (Der Kupfergehalt von Pflanzen und 

 Thieren in kupferreichen Gegenden. Archiv fiir Hygiene 27: 1. 

 1896). The last named found that specimens of plants grown in 

 ordinary soils may contain as much as 30 mg. of copper to each 

 kilo of dry matter while others in copper-rich soils yielded as 

 much as 560 mg. of the metal per kilo of dry matter. 



Carmel, Cal. 



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