CARNATION RUST 
This is a disease of European origin, which was first observed in this 
country in 1890. It rapidly developed in epiphytotic form, shortly appear- 
ing in every carnation house throughout eastern United States. It was 
for a decade the most destructive and most feared of carnation diseases, 
but is now enphytotic and rarely serious, due to the development of 
resistant varieties. It also affects some other species of the genus Dianthus 
and species in related genera. In Europe the cluster-cup stage of this 
disease is known, affecting Euphorbia gerardiana Jacq. 
SYMPTOMS 
Since the cluster-cup stage of the carnation rust is unknown in America, 
the disease will be studied only as it appears on the common greenhouse 
carnation. The red and black rust stages appear together and are so 
much alike that the symptoms they induce will be considered together. 
Both leaves and stems are affected. Study the materials provided and 
OBSERVE :— 
1. The pale-green or yellowish areas on the leaves; which 
surface? 
2. In some of these spots, dark-brown or black pustules,— 
sori of the pathogene. The lighter-colored ones are uredinia, the darker 
ones, telia. 
3. The arrangement of these sori within the lesion; scattered, 
confluent, linear? 
4. Some of the sori burst open exposing the dark-colored rusty 
spore-mass within; the ruptured epidermis forming a papery fringe. 
5. The sori on the stems; usually darker than those on the leaf. 
Stem-sori are largely telia. 
6. The general effect of the disease on badly rusted plants. 
Make DRAWINGS to show the characters of the lesions on leaves and 
stems. 
ETIOLOGY 
The causal organism is a urediniaceous fungus, Uromyces Caryophy- 
linus (Schrank) Winter. It is heteroecious, having all the spore-forms 
characteristic of the rust-fungi. 
Life-history. Being in this country a parasite of a greenhouse-crop, 
the fungus is able to propagate itself continuously through secondary 
cycles. The primary cycle therefore will not be here considered. 
The Secondary Cycles are all initiated by uredospores from sori on 
leaves or stems of living plants (except of course when aeciospores occur). 
They are constantly being initiated as uredospores are matured and 
disseminated. 
Scrape some of the uredospores from a sorus; mount and study. 
OBSERVE -— 
7. The form, size, color, thickness of wall and markings on the 
epispore. Treat some with acetic acid and see if the number and arrange- 
ment of the germpores can be determined. DRAw several uredospores. 
These uredospores are scattered by wind or splashed, in watering, to 
nearby healthy leaves and plants. They germinate very readily in water. 
Examine the germinating spores on the slides provided. OBSERVE :— 
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