RUST OF CEDAR AND APPLE 
This is a very common disease of the apple in many sections of the 
country where the red cedar grows. It is especially prevalent in the Mis- 
sissipp1 Valley, northeastern New York, New England, Virginia, West 
Virginia and other southern states. The effect of the pathogene on both 
hosts is very marked. 
Most of the rust diseases of rosaceous plants are harbored by some 
species of cedar during the winter. In the case of the rust here con- 
sidered, the pathogene overwinters on the red cedar, J: uniperus virginiana 
L. The summer form of the pathogene occurs on wild crab, Pyrus 
coronaria L., as well as on the cultivated apple. The rusts appearing 
on pear, quince and hawthorne are usually caused by species distinct 
from that causing the apple rust; all, however, are closely related. 
SYMPTOMS 
The symptoms differ strikingly on the two hosts. 
On the apple. The material provided was collected in midsummer. 
Examine the affected leaves and oBsERVE:— 
1. That the pathogene produces a leaf-spot. How does it 
differ from other leaf-spots? 
2. The differences in the character of the spot on the upper and 
lower surfaces as to color and definiteness of outline. 
3. The presence of black pimple-like structures on the upper 
surface,—the pycnia (spermagonia) of the pathogene, probably function- 
less male structures. 
4. The groups of brownish, somewhat cylindrical or fimbriate 
structures on the lower surface,—fruit-bodies called aecia (aecidia). 
SKETCH to show the above characters. 
The general effect of the pathogene is to give the trees a striking yel- 
lowish color in contrast to the dark green of the healthy trees nearby. 
Early defoliation follows severe infections. There is a marked variation 
in the susceptibility of varieties. Wealthy and Jonathan are especially 
susceptible. 
Lesions appear on the fruit when it is about one-fifth grown. They 
resemble those on the foliage. Examine diseased fruits provided and 
OBSERVE -— 
5. The color and location of the diseased area. 
6. The dwarfing effect on the fruit. Recall the effect on the 
leaf. 
7. The kinds of pathogene-structures developed in these lesions. 
DRAW a diseased fruit. 
On the red cedar. The material provided was collected in early spring 
(April). OBSERVE :— 
8. The large brown galls. Form, size, consistency, and surface 
characters. . 
9. The spore-cushions scattered over the surface,—the telia 
(teleuto-sori). ; 
10. The attachment and the relation of the gall to the twig. 
Each gall results from an enlargement of a single leaf, according to certain 
authors or of the stem in the axil of the leaf, according to others. 
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