ooi Univeisity of California PnhlicaUons in Agricultural Sciences [Vol. 1 



and Breiicliley^° to be confirmed in that opinion. The general 

 impression given by the reviewers is that so far as plants are 

 concerned, copper is to be regarded as a distinctly toxic sub- 

 stance. To quote Brenchley from the work above cited, for 

 example : ' ' Altogether, after looking at the question from many 

 points of view, one is forced to the conclusion that under most 

 typical circumstances, copper compounds act as poisons to the 

 higher plants, and that it is only under particular and peculiar 

 conditions and in very great dilutions that any stimulative 

 action on their part can be clearly demonstrated." This state- 

 ment is not qualified with respect to the kind of medium em- 

 ployed for testing the effects of copper on plants. But whether 

 it be applied to solution or to soil cultures, it would scarcely 

 seem to be adequately supported by experimental evidence, and 

 particularly is this true regarding soil cultures. In solution 

 cultures, copper in various compounds was found to be toxic 

 to the higher plants by Otto,^^ HaselhoffV" Coupin,^" Kanda,^* 

 True and Gies,^^ True and Oglevee,^** Jensen,^' Brenchley,^^ 

 Heald,^^ Harter,^" and Haywood.-^ While exceedingly high 

 dilutions of copper salts were employed by some of these in- 

 vestigators, the possibility still exists in tlieir work that the 

 merest traces of copper maj^ have acted as stimulants. More- 

 over, in the case of Jensen's work the evidence on the toxicity 

 of very dilute solutions of copper salts is really negative, since 

 he emphasizes principally the fact tliat no stimulation was 

 observed with CUSO4 in solution cultures. 



10 Inorganic plant poisons and stimulants, Cambridge, 1914. 



11 Ztschr. Pflanzenkrank., vol. 3, no. 6; Bot. Cent., 5G, p. 340; E. S. E., 

 5, p. 649. 



i2Landw. Jalirb., 21, p. 263; E. S. E., 3, p. 499. 



i3Comptes Eendus Acad. Sci., Paris, 127, p. 400; E. S. E., 10, p. 611. 



14 Jour. Col. Sci. Imp. Univ. Tokyo, 19, p. 47; Bot. Cent. 95, p. 538; 

 E. S. E., 16, p. 228. 



15 Bull. Torr. Bot. Club, 30, p. 390. 



16 Bot. Gaz., 39, p. 1; Science, 19, p. 421. 



17 Bot. Gaz., 43, p. 11. 



18 Inorganic plant poisons and stimulants, Caml^ridge, 1914. 



19 Bot. Gaz., 22, p. 125. 



20 U. S. Dept. Agr., Bur. PI. Ind., Bull. 79, p. 40. 



■ii IJ. S. Dept. Agr., Bur. Chem., Bulls, nos. 89, 113, and 113, revised. 



