MICHIGAN ACADEMY OF SCIENCE. 



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Figs. 10 and 11.) Usually the hyphae begin to come up through the 

 leaf surface on about the fourth day after inoculation. The hyphae 

 underneath the epidermis turn up and penetrate between the epidermal 

 cells and in some cases a hypha may be seen coming up through a stoma, 

 (PI. XIV, Fig. 10). The former method is much more common. The 

 hyphae once outside the leaf begin to swell at the tip and produce spores. 

 The process of spore formation will be described later. 



2. Morbid Physiology : 



The work of Levin (1916) with the Septoria leaf-spot diseases of 

 tomato had shown that the newly formed spots on the tomato leaves 

 transpired more than the healthy tissue. With old spots on the con- 

 trary no transpiration took place, and this is ascribed to the dead tissue 

 being cut off from the water supply. 



An experiment using the method described by Levin was set up to 

 find if in clover there was transpiration from diseased spots. A simple 

 potometer (modification of Ganong's) the construction of which may be 



Figure 14. Simple potometer. 



easily understood by referring to the diagram (Fig. 11), was used. Into 

 this was fitted a red clover leaf bearing 6-8 large, old disease spots, the 

 place where the petiole enters the tube being sealed by the application of 

 anhydrous lanolin. By careful manipulation, an air bubble was obtained 

 in the horizontal arm of the tube. A paper centimeter scale was then 



