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Felt-rust stage on currants and gooseberries. In the material of 
gooseberry and currant leaves provided, NoTE:-— 
11. The conspicuous hair-like growths,—the telia, often arising 
from the uredinia and more or less scattered over the entire under surface 
of the leaves. pRraw. In some cases the felt-rust stage accompanies 
the first uredina early in the summer but it is typically an autumnal stage, 
occurring in August and September. 
ETIOLOGY 
The blister-rust of five-needled pines is caused by the basidiomycetous 
rust-fungus, Cronartium ribicola Fischer von Waldheim. ‘This name is 
based on the telial stage. The aecial stages of rusts, forming blister-like 
aecia on the bark or needles of conifers, have all been placed in the form- 
genus Peridermium. The blister-rust of five-needled pines is commonly 
known in its aecial stage as Peridermium strobi Klebahn. 
Life-history. This pathogene is a heteroecious fungus Tequiring two 
very different hosts for the development of its complete life-history. 
All the spore-stages produced by rusts are formed by this fungus: aecia 
(I) on bark of pines; uredinia (II), telia (III) and promycelia (IV) on 
the leaves of currants and gooseberries. The pyenia (O) are produced on 
the pine previous to the appearance of the aecia. : 
Primary Cycles are initiated by the aeciospores produced in the 
aecia on the pine in early spring. When the peridium is ruptured, the 
aeciospores dust out and are blown about by the wind. 
Pathogenesis. The primary inoculum, aeciospores from the pine, 
must reach young leaves of currants and gooseberries in order to function 
in continuing the development of the fungus. The aeciospores cannot 
infect the pine. 
Mount some of the yellow powder from the aecia in potassium hydroxide, 
cover and examine with the microscope. OBSERVE:— 
12. The size, shape and color of the aeciospores; thickness and 
markings of the spore-wall. DRAW. 
The aeciospores, in the presence of moisture, germinate on the under 
sides of gooseberry and currant leaves and the germtubes penetrate into 
the stomatal cavities. After the establishment of a food-relation with the 
host-cells surrounding the sub-stomatal cavity, a mycelium is produced 
which spreads in a limited area. Within about two weeks after infection 
the uredinia are formed. In the material studied under symptoms of this 
stage, NOTE :— eco ce ee 
13. The general character of the uredinia in different stages of . 
development. 
14. The size, shape and color of the uredospores under the 
microscope. 
15. The thickness and markings of the spore-wall. 
DRAW a typical uredospore showing above points. hes 
In the prepared slides showing stained sections through uredinia, 
NOTE :— 
16. The epidermis of the leaf which was raised up and finally 
ruptured by the developing uredinium. 59 
17. The peridium enclosing the contents of the uredintum. 
