356 OHIO EXPERIMENT STATION: BULLETIN 214 
spores. In the treatment of tubers and rootsas the potato, etc., 
longer soakings with solution of formaldehyde or corrosive sublimate 
are required to kill not only external spores but resting forms of 
fungi such as sclerotia, etc. 
With soil treatments we have the problem of killing out soil 
infesting organisms such as nematodes or eelworms and Rhizoctonia, 
Botrytis, lettuce drop, etc., among the fungi. All these results are 
obtained by thoroughly steaming the soil. In a measure the same 
results are also obtained from a formaldehyde drench as elsewhere 
described. 
Fumigation for the destruction of seed infesting fungi or cutting 
infesting insects is of the same character and must be named here. 
The fumigation of nursery cuttings with hydro-cyanic gas is 
effective as is also the fumigation of stored grain with carbon 
bisulfid. We must also consider that wound coverings are methods 
of prevention in plant disease, since these coverings of asphaltum 
creosote, gas tar, paraffine and even of paint serve the purpose of 
excluding wound fungi which might otherwise cause serious decays. 
All these treatments that have just been enumerated apply to the 
treatment of the soil or of seeds and plants in resting condition. 
The great problem of keeping down infection during the growing 
period yet remains for the application of spray mixtures. 
SPRAYING WITH FUNGICIDES--INSOLUBLE COPPER COMPOUNDS 
The progress made in the control of plant diseases through 
sprays since Millardet’s discovery of Bordeaux mixture (bouillon 
bordelaise) near Bordeaux, France, in 1883 shows how great was 
then and is still, the need for effective fungicides. The materials 
from which Bordeaux mixture is made consist of copper sulfate 
(blue vitriol) calcium oxid and hydroxid (caustic lime) and water. 
In the making of the mixture the copper sulfate is dissolved in water 
and should be diluted with a considerable amount of water; the lime 
is slaked or converted into lime putty from which a milk of lime is 
prepared. These two mixtures with the copper sulfate in aqueous 
solution and calcium hydroxid in suspension, mixed together makea 
chemical reaction by which the calcium in the lime displaces in part 
the copper in the copper sulfate, forming on one hand calcium sul- 
fate or gypsum, and on the other the various combinations of lime 
with the metallic copper thus liberated. The actual reactions have 
been variously interpreted. More recent investigations show that 
several basic sulfates of copper and lime are produced. Whether 
any hydroxid of copper is produced has been questioned by Picker- 
ing, an English investigator. The light blue coloris due to suspended 
