each producing a short branch with a little sporidium, s.
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Fig. 282.—Germinating Teleutospore of Wheat Rust.
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Fig. 283.—Leaf of Barberry with Cluster-cups.
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Fig. 284.—Section through a Cluster-cup on Barberry Leaf.
A most remarkable circumstance in the life
history of the wheat rust is the fact that the mycelium
produced by the sporidium can live only in barberry leaves, and it follows that if no barberry
bushes are in the neighborhood the sporidia
finally perish. Those which happen to lodge on
a barberry bush germinate immediately, producing
a mycelium that enters the barberry leaf and
grows within its tissues. Very soon the fungus
produces a new kind of spores on the barberry
leaves. These are called æcidiospores. They are
formed in long chains in little fringed cups, or
æcidia, which appear in groups on the lower side
of the leaf (Fig. 283). These orange or yellow
æcidia are termed cluster-cups. In Fig. 284 is
shown a cross-section of one of the cups, outlining
the long chains of spores, and the mycelium in the tissues.
The æcidiospores are formed in the spring, and after they have been set free, some of them lodge on wheat or other grasses, where they germinate immediately. The germ-tube enters the leaf through a stomate, whence it spreads among the cells of the wheat plant. In summer one-celled reddish uredospores ("blight spores," red-rust stage) are produced in a manner similar to the teleutospores. These are capable of germinating immediately,