75 
Affected fruits may fall from the tree during all stages of the disease. 
Explain why. Whether or not they fall, there finally results a much- 
wrinkled dark-brown mummy. Examine the mummies provided and 
Pl. Ind. Bur. Bul. 93, pl. I, VI and VII. Read the descriptions. sKETCH 
to show a fallen and a hanging mummy. 
On the limbs. The lesions on the limbs are cankers. Twigs are wholly 
killed and are then said to be blighted. Examine the canker before you 
and OBSERVE :— 
7. The general appearance of the lesions as to color, size, shape 
and surface characters. Do you find evidence of a dead twig at the center? 
(See Pl. Ind. Bur. Bul. 44, pl. VII and Illinois Bul. 118, pl. land IV.) Make 
@ DRAWING of a typical canker. Young cankers begin as small, dark, 
sunken, sharply defined areas. (See Pl. Ind. Bur. Bul. 44, pl. IX.) 
ETIOLOGY 
The pathogene, now known as Glomerella cingulata (Stoneman) 
Spaulding and von Schrenk, is an ascomycetous fungus belonging to 
the family Gnomoniaceae of the Pyrenomycetes. Its conidial stage has 
long been known under several names, that usually applied to the fungus 
on the fruit being Gloeosporium fructigenum Berkley. 
Life-history. Extensive studies on the life-history of this fungus 
have been made, especially by American workers, so that the details are 
now well known. 
The Primary Cycle is very definite. There are many secondary ones 
during the season. 
Pathogenesis. The mummied fruits hanging on the trees and the 
cankers are the sources of the primary inoculum. The fungus hibernates 
in these, producing during the spring conidia in acervuli. Apparently 
ascospores, which may initiate the primary cycle, ordinarily play but a 
small réle in the life-history of this pathogene. Make crushed mounts 
of acervuli from the mummies or cankers provided and OBSERVE — 
8. The hyaline conidia; their form, granular contents, abundance 
and variation in size. DRAW several to show these points. 
These conidia, washed and splashed by the rains to young fruits, initiate 
primary infection. Study the germinating spores provided. OBSERVE:— 
9. The long septate germtubes; point of origin. _ 
10. The dark thick-walled appressoria formed at the tips of some 
of the germtubes. What is their function? (Compare Pl. Ind. Bur. Bul. 
44, pl. V.) pDRaw several germinating spores. 
The germtubes, directly from the spores or from the appressoria, 
penetrate the uninjured skin of the apple or gain an entrance through 
wounds and a mycelium is rapidly developed resulting, usually within a few 
days, in a distinct rot-lesion. Fruits generally affected are often in a 
conical region beneath a mummy or canker. Remove a bit of the diseased 
apple flesh with the forceps and stupDy:— ; 
11. The mycelium; its character and branching. pDRaw. 
The lesions soon begin to show developing fruit-bodies,—the acervuli 
of the conidial stage of the fungus. 
Study the diseased fruits provided. NoTE:— 
12. The location and concentric arrangement of the acervuli 
within the lesion. ; 
13. The different degrees of development of these fruit-bodies 
from the center toward the margin of the spot. 
