Studies on Fungicides — ITI 39 



parently the spores had absorbed, or otherwise removed from solution, 

 only a pari of the copper that they had dissolved. 



Crandall (1909:291) reports, "No evidence has been obtained in sup- 

 port of the suggestions of authors that solution of copper occurs through 

 the agency of germinating spores." However, no direct experiments on 

 which to base this conclusion are mentioned. 



Barker and Gimingham undoubtedly have undertaken the most exten- 

 sive investigations relative to the solvent action of fungus spores. In 

 one series of experiments (1911), spores of Penicillium glaucum were placed 

 in a 1-per-cent dextrose solution plus insoluble basic copper sulfate. 

 After a time this showed 0.0011 per cent of soluble copper, or twice as 

 much as the controls. Similarly, Penicillium spores were placed in a 

 dextrose solution, and, after fair growth, were filtered. The filtrate was 

 then added to the basic copper sulfate, and 0.0075 per cent of copper was 

 I nought into solution as compared with the control, which showed 0.0004 

 per cent. The authors, however, point out that the conditions were 

 abnormal in that the solvent action may have come from dead or dying 

 cells, and also that the culture reaction was acid. Hanging-drop cul- 

 tures of conidia of Nectria ditissima and Sclerotinia frvctigena were made. 

 In general, in the presence of no-excess-lime bordeaux (lOCuO, SO3) or 

 of ordinary bordeaux, there was little if any germination; while in the 

 filtrates from such compounds, there was usually good germination and 

 fair growth, though not so good as in the controls. But with uredospores 

 of Puccinia hieracea, in the presence of no-excess-lime bordeaux there 

 was some germination and fair growth, while in the filtrates and the con- 

 trols the percentage germination was high and the growth of germ tubes 

 vigorous. The authors state (pages 86-87 of reference cited) : 



The whole of these results tend strongly to support the hypothesis that certain fungi at 

 least are able to act on the insoluble copper compound sufficiently to poison themselves, 

 provided that they are associated closely enough with it: for in all cases copper was practically 

 absent, from (he filtrate before use, so that it was obviously the presence of the insoluble 

 compound which was necessary to give the mixture fungicidal properties. There appear to 

 be only two explanations to satisfy the results. Either the fungus spore in its dormant 

 condition or in the incipient stages of germination exerts a solvent action on the copper 

 compound: or the minute traces of that substance which can be present in a state of solution 

 act as a cumulative poison. 



In another experiment, no-excess-lime bordeaux was placed inside a 

 diffusion tube, and the filtrate on the outside. Nectria spores were sown 

 in each, and germinated well on the outside. A few germinated well on 

 the inside where they were not in contact with the copper particles, which 

 had, however, largely settled. Again, ao-excess-lime bordeaux was dried 

 on glass cover slips and suspensions of Nectria spores in distilled water 

 were added so that they overlapped the bordeaux films. The water was 

 allowed to evaporate and the cover slips were then placed in a moist 



