410 BOTANICAL GAZETTE [JUNE 
physiologists and chemists bearing on the subject under considera- 
tion. 
The extreme toxicity of copper to plants under certain condi- 
tions has been responsible, it would appear, for some assumptions 
on the part of investigators as to the similarity in the action of 
copper in solutions and in soils. Thus JoHNsoN, in his now classic 
work How crops grow, evidently assumes from the results obtained 
in solutions that copper is poisonous to plants even in very small 
quantities. Likewise the work of HEALD’ and Harter’ with plants 
grown in solutions shows copper to be extremely toxic to plants. 
The former found, for example, that 1 part of copper in 404,423 
parts of water was deadly to the garden pea (Pisum sativum), and 
that maize (Zea mays) seedlings are killed by the presence of 1 part 
of copper in 808,846 parts of water. OsTERHOUT* showed how water 
obtained from copper stills was poisonous to certain of the lower 
plants when containing merely traces of copper, and Haywoop, 
in the work above mentioned, states that in preliminary work with 
plants in soils containing copper, the growth of wheat and rye is 
“interfered with by the presence of 2.1 parts of soluble copper 
per million parts of earth in one soil, and by 3.5 parts of soluble: 
copper per million parts of earth in another soil.” 
Some striking results on the effects of copper on plant growth 
which date back much farther than the last discussed were those 
obtained at the New York‘ and the Iowa’ Experiment stations. 
It is a curious coincidence that both of these investigations were 
reported in the same year (1892), and they were both the result 
of the fungicide investigations in which it appeared of interest 
to ascertain how the continued use of fungicides would affect the 
soil in its productive capacity. In the New York bulletin, Part I 
of which is devoted to the subject in question, we find that among 
peas, wheat, and tomatoes, which formed the test plants, a resistance 
was noted to as much as 2 per cent and 5 per cent of CuSO, of the 
t Bot. Gaz. 222125. 1896. 
2 Bur. Pl. Ind., U.S. Dept. Agric. Bull. 79. p. 40. 
3 Bor. Gaz. 44:272 (footnote). 1907. 
4N.Y. Exp. Sta. Bull. 41. 1892. 
5 Iowa Exp. Sta. Bull. 16, 1892. 
