58 S. E. A. McCallan 



A study of the results given in table 10 shows that rain water does not 

 allow as high a percentage of germination of the spores of Sclerotinia 

 americana as does distilled water. No explanation of this can be given. 

 This difference is evidenced, however, in both the experiments. The 

 distilled water in these experiments shows a little more solvent action 

 than did that in the previous ones. However, the difference is but small. 

 The rain water appears to possess a greater solvent power than does the 

 distilled water. 



It should be noted that, in all cases, spores placed directly on the sprayed 

 slides were completely inhibited from germination. These slides had 

 been exposed in water to the action of the air for periods of from 5 to 9 

 days. This bears out a previous conclusion that the presence of the 

 insoluble copper protectant is sufficient to inhibit germination, and shows 

 that the copper is not appreciably leached out by long exposure to wetting 

 with well-aerated water. 



A second conclusion to be drawn from these experiments is that dis- 

 tilled water, either standing undisturbed or receiving a continuous pas- 

 sage of air, does not promote the solution of copper to an effective extent. 



Thirdly, rain water exhibits greater solvent action than does distilled 

 water. It is difficult to determine how much of this apparent toxicity is 

 actually due to the solvent action of the rain water, for the germination 

 is also slightly reduced in pure rain water. In any case, the results of 

 the experiments show that sufficient copper is not brought into solution 

 by this means to more than slightly inhibit the germination of the spores. 

 This is especially significant when it is realized that here a very large 

 amount of carbon dioxide came in contact with the insoluble copper 

 for long periods of time. It is believed, therefore, that under natural 

 conditions atmospheric agencies cannot bring about the liberation of 

 copper necessary to kill or to effectively inhibit the germination of spores. 



Spore excretions 

 The solvent action of filtrates from suspensions of germinating spores 



Hypothesis. The hypothesis considered in the following paragraphs is 

 essentially that of Wallace, Blodgett, and Hesler (1911:186), namely, 

 " that the germinating spore secretes a dissolving agent which acts on 

 the insoluble fungicide to bring small quantities of the same into solution " ; 

 that is, water in which spores have germinated possesses dissolving powers 

 greater than that of pure water. 



Wallace, Blodgett, and Hesler (1911) performed a few preliminary 

 experiments with lime-sulfur. They placed spores of Sclerotinia cinered 1 

 in water in a watch glass, allowed them to germinate for three days, and 

 then filtered the suspension. This filtrate they considered to consist 



2 Presumably S. americana. 



