72 S. E. A. McCallan 



THE NATURE OF THE SPORE EXCRETIONS 



In the foregoing studies, experimental evidence seems to establish the 

 presence of an excretion from the spores which exerts a solvent action 

 on the insoluble copper protectant, thus freeing soluble copper. It is 

 hoped that, at some future date, investigations regarding the nature of 

 the spore excretions may be undertaken. At this time only some pre- 

 liminary studies will be mentioned. 



None of the investigators who have been inclined to the spore-excretion 

 hypothesis appear to have attempted a study of the nature ef the spore 

 excretions. In the case of germinating seeds and the roots of young 

 plants, Barker and Gimingham (1914 a) state that carbon dioxide is an 

 active agent. However, they submit no experimental evidence. Other 

 workers also have suggested the possible role of carbon dioxide. 



Attempts have been made to determine the hydrogen-ion concentration 

 of the water in which spores were germinating. Spores of Sclerotinia 

 americana were allowed to germinate in distilled water for varying periods 

 of time. Hydrogen-ion determinations were attempted of suspensions 

 of germinated and ungerminated spores and of filtrates from each. Two 

 standard methods were used — that of the quinhydrone electrode, and 

 that of indicators. The results were very unsatisfactory. No constant 

 readings could be obtained, nor could any consistent difference between 

 these solutions and distilled-water controls be demonstrated. Apparently 

 these solutions are almost, if not entirely, devoid of buffer action, and 

 accurate determinations of the hydrogen-ion concentration are imprac- 

 ticable if not impossible. One interesting observation was made, however, 

 namely, that in the process of filtration the filtrate is rendered more alka- 

 line, usually to the extent of pH 0.3 to 0.5 more than the original solution. 



Following the failure to obtain satisfactory results in the hydrogen-ion 

 determinations, some preliminary tests were made in determining total 

 acidity by titrations. To insure a very sensitive test, the method of 

 Rosa, Vinal, and McDaniel (1913, 1914), employing iod-eosine as the 

 indicator, was used. 4 Five-cubic-centimeter samples of the spore-excretion 

 water were taken, and were titrated with N/1000 NaOH. Hydrogen-ion 

 determinations of samples of distilled water which had been exposed 

 for the same length of time that the spores were allowed to germinate — 

 from 16 to 28 hours — also were made. The solutions were not filtered. 



The distilled-water controls required from 13/20 cubic centimeter of 

 N/1000 NaOH through neutrality, to 4/20 cubic centimeter of N/1000 

 HC1, for neutralization to iodeosine. The spore-excretion solutions were 

 found to be more acid than the water, and a fairly constant difference 

 of about 5/20 cubic centimeter of N/1000 NaOH was observed. That is, 

 the spore excretions had an acidity equivalent to N/20,000 HC1. 



'The writer wishes to acknowledge his indebtedness to Dr. A. S. McDamel for assistance and advice in 

 performing these tests. 



