BLACK STEM-RUST OF CEREALS AND GRASSES 
There are many rust diseases of cereals and grasses. The black stem- 
rust is perhaps of greater economic importance than any of the others, 
especially on wheat. It is one of the earliest-recorded rust diseases and 
the subject of many researches by mycologists and plant pathologists. 
Early in the spring it may affect the barberry (Berberis vulgaris L.). 
At the same time or later in the season it appears on wheat, oats, barley, 
rye and many other grasses. On cereals and grasses it is characteristically 
a stem-rust. 
SYMPTOMS 
This disease is far more injurious to cereals and grasses than to the bar- 
berry. The signs and symptoms exhibited by rust diseases are associated 
with certain distinct spore-producing stages of the causal fungus. In the 
case of the black rust of cereals there are three: the cluster-cup stage, the 
red rust stage and the black rust stage. 
Cluster-cup stage. The leaves and flower-racemes of the barberry are 
the organs affected. Examine the leaves provided and OBSERVE :— 
1. The small spot-lesions; size, location, color both above and 
below, and the thickening of the leaf-tissues in the lesion. The disease 
exhibits distinct metaplastic effects on this host; there is a slight over- 
growth of affected tissues. 
2. With the hand-lens, the tiny dark amber or nearly black 
pimples embedded in the tissues of the upper surface,—the pycnia (sper- 
magonia), functionless structures of the pathogene. They normally 
accompany or precede, in the same lesion, the aecial fruit-bodies next to 
be observed. : ; 
3. On the lower surface, the sunken cups, exposing their yellow 
spore-masses. These are the aecia or cluster-cups. 
Make prawincs to show the cluster-cup symptoms on both surfaces 
of the leaf. 
Examine the diseased flower-clusters. OBSERVE :— 
4. The swollen and malformed flowers and pedicels; color of 
the affected organs. 
5. The abundantly developed aecia. Are pycnia present? 
SKETCH a diseased flower cluster. 
Red rust stage. Examine the specimens of diseased wheat or oats 
provided and OBSERVE :— 
6. The large reddish yellow pustules scattered over the leaf- 
Te Camas uredinia; not usually so common nor so numerous on the 
ades. 
7. The size, arrangement and relation of these pustules to the 
host-tissues. Note the torn edges of the epidermal covering and the dusty 
spore-mass of the ruptured uredinia. 
8. The effect on the host-tissues; color effects. 
SKETCH a rusted leaf-sheath to show the symptoms of the red rust stage. 
Make a DRAWING of one of the uredinia as it appears under the hand-lens. 
Black rust stage. This develops during the latter part of the growing- 
season along with the red rust stage so that the two are often observed 
together on the leaf-sheaths and stems. In the material provided, 
OBSERVE :-— 
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