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‘Remove one of the healthy leaves and NoTE:— 
11. The size, form and relation to the twig. 
SKETCH a normal leaf and a diseased or galled leaf; maintain proper 
proportions. 
The most striking sign of this disease on the red cedar is exhibited during 
warm spring rains in April and May. From the telia scattered over the 
gall, long yellow gelatinous teliospore-masses protrude, giving the effect, 
from a distance, of large yellow fruits; whence the popular names cedar- 
apples and cedar-flowers. 
ETIOLOGY 
This disease is caused by one of the Uredinales, Gymnosporangium 
Juniperi-virginianae Schweinitz. As already noted, the pycnial stage (O) 
and the aecial stage (I) occur on the leaves and fruits of the cultivated 
apple and wild crab. The telial stage (III) is found on the red cedar. 
A urédinial stage (II) is wanting. 
Life-history. The apple rust-fungus continues in close association 
with the living tissues of its hosts throughout its entire life-history. 
Primary Cycle 
Pathogensis. The inoculum for the primary cycle consists of 
sporidia which are produced on the red cedar. They are developed on a 
promycelium which in turn arises from a teliospore. Moisture of six or 
more hours duration is necessary for sporidial formation. As soon as 
the humidity decreases sufficiently to cause appreciable evaporation, 
the sporidia are forcibly ejected. This occurs from April to June. 
Sporidia are carried to the apple by the wind. Germination follows 
within a short time in the presence of moisture. Two types of germina- 
tion occur; one in which germtubes develop directly from the sporidia, 
and the other in which secondary sporidia are formed on a short germtube. 
The latter type is more common. (See Phvtopath. 3:282, fig. 1, and Ne- 
braska Rept. 22, pl. III, fig. 5; or Virginia Tech. bul. 9, fig. 9.) copy to 
show types of sporidial germination. 
The germtube arising from the secondary sporidium penetrates the 
cuticle. In the case of the leaf, this occurs on the upper surface. The 
mycelium developed from the sporidial germtube ramifies through a 
limited area of the leaf, with the result that tissue-changes are effected 
and certain fruit-bodies (O and I) are developed. Examine the apple 
leaves again, using hand-lens. oOBSERVE:— 
12. The pycnia on the upper surface of the leaf; their form and 
distribution. 
13. The aecia on the lower surface of the leaf; their form, 
distribution and size. The long exerted peridium (aecial-wall),—a promi- 
nent character of aecia of this fungus. Rust-fungi showing aecia with 
such peridia belong to the form-genus, Roestelia. Accordingly the apple 
rust-fungus was formerly called Roestelia Pyrata (Schw.) Thaxter. 
Make enlarged prawincs to show the pycnia and aecia as they appear 
under the hand-lens. 
Mount in potassium hydroxide some of the peridial cells and aeciospores 
from the aectum. Study and praw to distinguish them. 
Examine prepared slides showing sections through lesions on an apple 
leaf. OBSERVE :—~ 
14. The abnormal tissue-developments. Which tissues are 
involved? How affected? 
