68 S. E. A. McCallan 



TABLE 17. Percentage Germination of Sclerotinia Americana Conidia at Varying 

 Distances from an Area of Dried Bordeaux Mixture (Spore-Suspension Drops 

 and Bordeaux Drop Placed in a Petri Dish and the Whole Covered by a Film 

 of Water) 



experiment was carried, in which the filtrate from water standing on a 

 surface sprayed with bordeaux mixture was tested. The age of the spores 

 was 6 days. 



Discussion. The results from the tests of the spores placed on the 

 slides at varying distances from the bordeaux mixture, are very inter- 

 esting. It can be seen that as the distance from the bordeaux and the 

 number of spores are increased, so the percentage and the quality of 

 germination increase. With the petri dishes, the volume of water and 

 the relative distances are sufficiently great so that the differences in per- 

 centage and quality of germination are not so pronounced. 



Undoubtedly the filtrate from water standing in bordeaux mixture is 

 slightly toxic. However, as has already been pointed out, it is believed 

 that this toxicity is due to certain soluble calcium compounds present, 

 and perhaps also to the alkalinity of the filtrates. A point that seems 

 to- substantiate this is the apparent normal appearance of the contents 

 of ungerminated spores, which is characteristic of inhibition by calcium. 

 Spores killed or inhibited from germination by copper show a very decided 

 precipitation of their contents. 



All of these experimental results demonstrate most clearly the fact that 

 direct contact is not necessary in the toxic action of bordeaux mixture on 

 spores. It is evident that the spores may be killed, or at least inhibited 

 from germination, while at some considerable distance from the particles 

 of bordeaux. A factor influencing this toxicity is the number of spores 

 present. It is possible, either that the solvent spore excretions can 

 operate over a wide area, acting on bordeaux particles to liberate copper 

 by which the spores themselves are ultimately killed, or that the cumula- 

 tive toxic action may account for their death. Or, again, both conditions 

 may bring about this result. It seems difficult to conceive of such minute 

 traces of copper — as required by the cumulative-action hypothesis — 

 diffusing at such a rate as to inhibit the germination of the distant spores. 



