Figs. 222-224.—Puccinia graminis (wheat rust).
(After Marshall-Ward.)
408. How the fungus gets from the wheat back to the barberry.—If these sporidia from the teleutospores are carried by the wind so that they lodge on the leaves of the barberry, they germinate and produce the cluster-cup again. The plant has thus a very complex life history. Because of the presence of several different forms in the life cyle, it is called a polymorphic fungus.
The presence of the barberry does not seem necessary in all cases for the development of the fungus from one year to another.
409. Synopsis of life history of wheat rust.
Cluster-cup stage on leaf of barberry.
Mycelium between cells of leaf in affected spots.
Spermagonia (sing. spermagonium), small flask-shaped bodies sunk in upper side of leaf; contain “spermatia.”
Æcidia (sing. æcidium), cup-shaped bodies in under side of leaf.
Wall or peridium, made up of outer layer of fungus threads which are divided into short cells but remain united.
At maturity bursts through epidermis of leaf; margin of cup curves outward and downward toward surface of leaf.