Studies on Fungicides — III 41 



levis. Bordeaux mixture dried on glass slides was exposed to the rain 

 and dew to test the effect of exposure. Spores were then placed on the 

 slides, and, though toxicity was evident, it was but very little more pro- 

 nounced than in the unexposed controls. The supernatant water from 

 exposed bordeaux mixture was found non-toxic. The toxicity of lime- 

 water was investigated, and the alkalinity was found to be sufficient to 

 inhibit the germination of the spores. The effect of distance from a 

 bordeaux film also was studied. Spores of Phytophthora and Sclerotinia 

 were sown on glass slides at certain distances from films of ordinary bor- 

 deaux or no -excess-lime bordeaux. It was found that the spores nearest 

 the films, that is, within 1 millimeter, did not germinate. But as the 

 distance from the bordeaux film was increased, so the percentage of germi- 

 nation and the growth of germ tubes increased. Copper wire also was 

 found to inhibit the germination of these spores if they were present in its 

 immediate neighborhood. Lutman is inclined to the view that the copper 

 salts formed in bordeaux mixture are, when moistened, very slowly soluble 

 (pages 34-35 of reference cited). He planned no experiment, however, to 

 demonstrate this. His final conclusions are: 



1. The fungus spores are killed by contact, either: 



(a) with the bordeaux film, giving off free copper; or, 



(b) with the alkaline solution derived from some of the lime particles. 



2. The spores are inhibited from germination if they are in the region either of the bordeaux 

 film or of the lime particles. 



Cerasoli (1921) placed grape leaves which were, respectively, healthy, 

 slightly affected with mildew, and withered with mildew — the last- 

 named two being well covered with fungous growth — in distilled water, 

 care being taken to cover the leaf blades only. After some days of expo- 

 sure to the air, it was found that onty the water containing healthy leaves 

 gave a neutral reaction, the water in the other cases being more or less 

 acid. The acidity was most pronounced with the leaves having the 

 greatest amount of fungous growth. From this Cerasoli concludes that 

 the solution of the copper salts is due to very weak acids or acid salts 

 secreted by the parasite during its entry into the tissues, and that this 

 acidity would easily react on the colloidal copper hydrates which he 

 claims are formed in bordeaux mixture, thus giving rise to copper ions 

 to which the fungicidal action supposedly is due. 



Schmidt's work (1924) has already been discussed under atmospheric 

 agencies. He was unable to demonstrate the secretion of solvent sub- 

 stances from spores of Botrytis, Aspergillus, Monilia, Fusicladium, and 

 Trichothecium, that would dissolve the copper in copper hydroxide or 

 bordeaux mixture. 



The evidence to be derived from the literature relative to the hypoth- 

 esis of fungous excretions is very conflicting. Some investigators ap- 

 parently have clearly demonstrated this solvent action. Others have 



