EXPLANATION OF PLATE I. 



The Fungus of Black Knot. (Plowrightia Morbosa (Sz.) Sacc.) 



Fig. i. Diagrammatic representation of a section through three perithecia con- 

 taining spore sacs (asci). x 72.* 



Fig. 2. Two sacs containing ripe spores, ami two sterile threads (para- 

 physes). x 940. 



Fig. 3. Four winter spores (ascospores), germinating in water ; a, after one 

 day; b, after two days, x 940. 



Fig. 4. Six pycnospores from a knot; a, just placed in water; b, after one day; 

 c, after two days in water, x 940. 



Fig. 5. Six pycnospores from a pycnidium developed on gelatine from winter 

 spores; a, three fresh spores; b, a spore after one day in water; 

 c, a spore after two days in water; d, a spore after two days on 

 nutrient gelatine, dx 540; others x 940. 



Fig. 6. Three summer spores (conidia), with two of the threads on which they 

 are borne, x 940. 



Fig. 7. Three summer spores beginning to germinate after one day on nutrient 

 gelatine, x 940. 



Fig. 8. Threads bearing new crop of summer spores produced on gelatine 

 culture of summer spores from young knot, shown in Figs. 6 and 

 7. x 540. 



Fig. 9. Surface view, from above, of a pycnidium developed on gelatine from 

 winter spores, x 350. 



Fig. 10. Vertical section through such a pycnidium, showing origin of spores. 

 x 350. 

 Drawn chiefly from a single section, but completed in some details 

 from others. The threads about the mouth are not shown in the 

 section. 



* The number given after each figure represents the degree of magnification of the original 

 drawing, which has been reduced about one-third in this plate. The magnification of the figures, 

 as here given, is therefore about two-thirds of that indicated by the printed numbers. 



