1902] TOXIC PROPERTIES OF COPPER COMPOUNDS 27 
Copper occupies an intermediate position in regard to toxic 
value for the mold fungi.’ It is surpassed more than a hundred- 
fold by mercuric chlorid, silver nitrate, and potassium chromate 
and bichromate. It is a little less toxic than nickel and a little 
more so than cobalt; distinctly more toxic than iron and the 
mineral acids; twelve times as toxic as zinc; and about eighty 
times as toxic as ethyl alcohol. Its great superiority as a fungi- 
cide lies in its cheapness, the tenacity with which its hydroxid, 
when properly prepared, adheres to the foliage of plants, and, 
as I shall show later, the solubility of its hydroxid in the pres- 
ence of or by means of substances found alike in the cell sap of 
the host plant and of the parasite, but more especially the latter. 
For a detailed description of the method of using the Van 
Tieghem cell for work of this kind the reader is referred to my 
article in a former issue of this journal. I may add that the 
method has proved eminently satisfactory for various physio- 
logical and toxicological studies with pure cultures of fungi, 
yeasts, and bacteria. 
Precautions for sterilizing were observed throughout the 
study, except with a few cultures of hymenomycetes. The 
spores used, of such fungi as can be normally matured in arti- 
ficial culture, were taken from pure cultures frequently renewed 
to insure high vitality. Rhizoctonia and currant cane blight 
cultures were inoculated with mycelium taken from fresh pure 
cultures. With Hypholoma and Coprinus,’ spores taken from 
plants growing under natural conditions were used. Naturally, 
every precaution was taken to avoid contamination, and on the 
whole very little difficulty was experienced on this account. 
It is very important in any quantitative study of this kind to 
SCLARK, J. F.: On the toxic effect of deleterious agents on the germination and 
development of certain filamentous fungi. Bot. Gaz. 28: 289-327, 378-404. 1900. 
S CLARK, J. F.: Bot. Gaz. 28: 293. 1900. 
71 beg to acknowledge my indebtedness to Dr. Margaret C. Ferguson, of Cornell 
University, who supplied me with the spores of Hypholoma and Coprinus, and to 
whose studies in the germination of the hymenomycetes I am indebted for the 
knowledge that they would be satisfactory for germination purposes in the media 
used, 
