83 
10. The blossom-end of the fruit, a type common in Missouri 
and other regions. 
DRAW from illustration specimens or from figures in the bulletins. 
After a month or so the entire fruit becomes a waxy and finally a dry 
mummy which may fall or may hang on the tree for a year or more. Study 
specimens provided and show in a DRAWING the character of these mummies. 
ETIOLOGY 
The name of the pathogene is Physalospora Cydoniae Arnaud. Until 
recently, it was known as Sphaeropsis Malorum Berkley which name is 
most commonly found in literature. The pathogene is very closely related 
to Guignardia Bidwellit (Ellis) Viala and Ravaz, the cause of black rot 
of grapes. Both organisms have similar perithecial and pycnidial stages. 
Life-history. This pathogene is evidently a facultative parasite. 
It develops most vigorously as a saprophyte on dead plant-tissues. It 
depends almost entirely on its asexual spores for propagation. The 
perithecial stage appears but rarely, at least in northern United States. 
The Primary Cycle is initiated by pycnospores, or by the ascospores, 
when the latter are produced. Only the former will be considered here. 
Pathogenesis. The fungus passes the winter as pycnospores in 
pycnidia and as mycelium in the cankers from which pycnidia with pycno- 
spores are produced. Remove several of the pycnidia from the cankered . 
bark provided and crush in a drop of water on a slide. Examine under the 
microscope and OBSERVE :— 
11. The great number of pycnospores; their color, size, shape 
and septation. DRaw to show variations in the spores. 
These -pycnospores constitute the chief primary inoculum. Washed 
by rain or possibly carried by insects to leaves or to wounds in the fruit 
or to dead tissue in the bark of the limbs, these spores germinate and ini- 
tiate the first infections. Study the germinating spores provided and 
OBSERVE :-— 
12. The long germtubes; color, contents, septation and branch- 
ing. Howmanyfromeach spore? DRAW. 
From the infection-court the mycelium penetrates in various directions 
into the living tissues, killing them as it spreads. 
To study the mycelium in the tissues, mount a bit of the rotted fruit 
well teased apart, or study prepared slides.of leaf-lesions in surface view, 
or sections through diseased bark. OBSERVE:— 
.13. The color, size, septation and manner of branching. How 
does this mycelium compare with the germtubes from the pycnospores? 
14. The relation of the mycelium to the host-cells (best seen in 
rotted fruit-tissues); inter- or intracellular? Are haustoria developed? 
(See Cornell Bul. 379, fig. 31.) 
DRAW to illustrate the character of the mycelium in the tissues. 
The mycelium near the center of the lesion soori begins to form gnarls 
of hyphae which rapidly develop into pycnidia containing pycnospores. 
(See Cornell Bul. 379, fig. 23.) Study the sections (freehand or prepared) 
through pycnidia. OBSERVE:— aor. ; 
15. The dark globose structures, seen in longisection; their 
relation to the tissues in which embedded; the ostiola. 
16. The structure of the pycnidial walls; origin and shape of the 
conidiophores; the spores and manner in which formed on the conidio- 
