256 ESSENTIALS OF BOTANY 



one is known as the duster-cup stage and the others as red 

 rust and hlack rust, according to the usual approximate 

 color of the spores. The rust called Pucoinia graminis, 

 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. 



Fig. 181. A Cluster-Cup of Anemone Rust (Puccijii'a/usca). (x 120.) 

 6, chains of spores; p, the covering oi per idium of the cup; h, hyphse. 



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 cu-ps (cecidia ; singular cecidium). Are 

 they on the upper or lower surface of the leaf ? 



(b) The number of cups in a cluster. 



(c) The form, size, and color of the cups. 



330. 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.^ 



1 If desired, prepared slides can be bought of tlie dealers. 



