MICHIGAN ACADEMY OF SCIENCE. 225 



to that of Anderson and McClintic for disinfectants might be worked 

 out for fungicides. The attempt has been made, therefore, to perfect 

 a satisfactory method, by means of which the relative values of various 

 substances used as fungicides can be determined in terms of a copper 

 sulphate solution of a standard strength. It is necessary to point out in 

 this connection that this method is wholly arbitrary and that the many 

 obscure chemical changes which may take place in fungicides (especially 

 lime sulphur), when used in this way, have not been studied. No attempt 

 has been made to determine the chemistry of the toxic effect on fungus 

 spores of the several solutions utilized. Definite and uniform results 

 under fixed conditions have been sought but the physiological and 

 chemical reasons for these results have not been considered within the 

 scope of the present work. 



In order that any method may become effective different workers must 

 follow definite standards such as this paper attemi)ts to establish. One 

 of the first factors to be taken into consideration is the test organism. 

 It was desirable, however, that the forms should be those producing 

 well known diseases, that they should grow abundantly and rapidly in 

 culture with a large spore production, and that growth in culture should 

 present definite and quickly recognized characteristics. Four organisms 

 were selected which seemed to offer certain of these advantages : 

 Sclerotinia fructigena (Pers.) Schi from apple, Glomerella rufomaculans 

 (Berk.) S & S., Rhizopus nigricans, Ehr. and Endothia parasitica 

 (Murrill) Anderson. The first one of these to be "eliminated was S. 

 fructigena because the lightness of the spores prevented them from going 

 into suspension well. Rhizopus nigricans offered many advantages but 

 its extreme resistance to the action of the fungicides used and to the 

 copper sulphate standard led to its being discarded. G. ruformaculans 

 proved to be very satisfactory in many respects, an important objection 

 to its use being the probable existence of strains physiologically different. 



For the test of this organism a culture was isolated from fruit taken 

 from the North Carolina State College orchard and another was received 

 from the Department of Botany of the Massachusetts Agricultural 

 College. Table No. 3 shows the differences in resistance of the two 

 cultures. 



