48 



S. E. A. McC ALLAN 



In order that the relations between the number of spores and the total 

 amount of copper may be the more clearly shown, figure 3 has been con- 

 structed from figure 2. In figure 3, milligrams of copper per liter of solu- 

 tion are plotted against number of spores, and four germination curves 

 — 0, 5, 50, and 90 per cent — as derived from figure 2 are drawn. 



O.O Ol O.Z O.d 0.4 0.5 0.6 0.7 O.ti 0<j /(J 



M////gran?s copper per £/Zer 



Figure 3. toxicity of dilute copper-sulfate solutions to the conidia 

 of sclerotinia americana 



Thus these are shown to be straight-line relations; that is, for a given 

 percentage of germination the number of spores is directly proportional 

 to the concentration of copper. This, of course, assumes that the volume 

 of copper-sulfate solution is constant and small. In other words, there is 

 a direct proportion between the number of spores and the total amount of 

 copper for a given percentage germination. 



In the study of the volume of solution, some difficulty was experienced. 

 The spores will germinate well only in small volumes of water. In large 

 volumes the oxygen relations appear unsatisfactory. A " drip system " 

 was finally devised for a study of the larger volumes. Essentially this 

 consists in the dripping of a large volume of solution over the spores, 

 which are held in very shallow petri dishes. The control spores give 



