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WHEAT RUST © 233 
Barberry. These cups are at first internal rounded 
bodies, in which spores (conidia) develop in chains, 
at length bursting through the lower epidermis. The 
spores quickly drop out and are carried away by the 
winds. This stage is known as the cluster-cup stage, 
and the spores as aecidiospores, or aeciospores. 
396. Associated with this cluster-cup stage there are 
usually flask-shaped structures known as spermogones or 
pycnia, in which minute spores or spore-like bodies 
(pyeniospores) are produced. They resemble the struc- 
tures which produce sperms in the Disk Lichens. If 
they have a similar function in the rusts it has not yet 
been demonstrated. 
397. (II) The aeciospores falling upon a wheat plant 
germinate there and penetrate its tissues, through the 
stomata, sending haustoria into the cells. After a few 
days, if the weather has been favorable, the parasite has 
grown sufficiently to begin the formation of large red- 
dish spores (uredospores, or urediniospores) just beneath 
the epidermis, which is soon ruptured, exposing the 
spores in reddish lines or spots upon the stems and leaf 
sheaths. This is the Red-rust stage, so common before 
wheat-harvest. These red spores fall easily, and quickly 
germinate on wheat again, producing 
more Red rust, and so rapidly increasing 
the parasite. 
398. (III) Somewhat later in the season 
the parasitic filaments which have been 
producing Red-rust spores begin to pro- 
duce the dark-colored, thick-walled, 
2-spored bodies characteristic of the 
Black Rust. Each 2-spored body consists of a contin- 
uous wall tightly enclosing the two spores, here called 
*‘teliospores.”? Being thick-walled, these spores endure 
