256 ESSENTIALS OF BOTANY 
one is known as the cluster-cup stage and the others as red 
_rust and black rust, according to the usual approximate 
color of the spores. The rust called Puccinia graminisa, 
growing on wheat, has its cluster-cup stage on the leaves 
of barberry in June. The spores from the cluster-cups 
are carried by the wind to the wheat, where they germi- 
nate and in a few days produce the red rust. A little 
later the black spores appear, produced by the same myce- 
lium. This growth is chiefly upon the stems and sheaths. 
Fic. 181. A Cluster-Cup of Anemone Rust (Puccinia fusca). (x 120.) 
s, chains of sporés; p, the covering or peridium of the cup; h, hyphae. 
329, Cluster-Cup Stage, Gross Structure. — Procure if possible fresh 
specimens of infected barberry leaves. If these are not available, 
dried leaves soaked for a short time in water or (still better) leaves 
preserved in alcohol may be used. With the magnifying glass note : 
(a) The occurrence of the cups (ecidia; singular e@cidium). Are 
they on the upper or lower surface of the leaf? 
(6) The number of cups in a cluster. 
(c) The form, size, and color of the cups. 
380. Cluster-Cup Stage, Minute Structure. — Cut a thin section of 
a leaf through a cluster of cups. This can best be done by holding 
the portion of leaf to be sectioned between two pieces of elder pith.? 
1If desired, prepared slides can be bought of the dealers. 
