112 THE AMERICAN MONTHLY [June 



Authorities. — In addition to the authorities cited last 

 month, by Pim, Griffiths names : Saccardo's Sylloge Fun- 

 gorum, the North American Pyrenomycetes by Ellis and 

 Everhart ; Parasitic Fungi of Illinois by T. J. Burrill ; 

 Uncinula by F. D. Kelsey ; papers by R. A. Harper and 

 by F. D. Kelsey. 



Technique. — A hand lens is useful in making collec- 

 tions of affected leaves. Having gathered pea leaves af- 

 fected by mildew, soak in a 5 to 10 per cent solution of 

 caustic potash for 15 minutes and wash. This will enable 

 you to remove the mycelial film from the leaf if you 

 scrape a spot lightly. With scalpel or forceps pull off 

 the film and mount in water, straightening out all folds. 

 Use low power and then higher powers to examine with. 



There will be seen the threads of mycelium as in fig. 1; 

 the swellings called haustoria as in figs. 2, 3, 4. It was 

 these by which the mycelium anchored itself to its host 

 and sapped its vitality. From the horizontal mycelium 

 grow the conidia-bearing hyphae as in fig. 5. The outer- 

 most ripens and drops off freeing a spore (fig. 6). 



Later in the season similar treatment and a mount in 

 dilute alcohol will reveal some perithecia, or little black 

 specks (figs. 7, 9, 10, 11, 11, 13). Different genera have 

 perithecia of different kinds and numbers of cells in 

 which asci are produced. 



Contents of the Plate. 

 Figs. 1 (x 340), mycelium. 

 Figs. 2, 3, 4, (x 340), haustoria. 



Figs. 5 (x 340), 6 (x 480), conidiophore and conidial spore. 

 Figs. 8, 14, 16, 17 (x340), asci. 



Figs. 1, 10,11 (x 170), 9 (x 340), 12, 13 (x 480 ) perithecia. 

 Figs. 15, 18, (x 480), ascospores. 



Species Shown. 



Erysiphe graminis D C. Figures 1-8 (mycelium, haus- 

 toria, conidiophore, conidial spore, perithecium, ascus). 



Sphaerotheca castagnei Figs. 9,16 (perithecium, ascus). 



