418 CLOVER-RUST. 



the dead stem. These spores germinate the next spring, when, 

 they produce secondary spores that fire said by an English ex- 

 perimenter to infect very young grass leaves, in which they form a 

 mycelium that quickly fruits in red rust. The winter-spores have 

 long been held to produce a mycelium in young barberry leaves, 

 on which the common yellow cluster-cups appear as a result, — 

 their spores again attacking grasses and forming a mycelium 

 that bears little of the red rust, but fruits almost exclusively by 

 winter-spores. 



Other grasses are subject to the attacks 

 of rust-fungi belonging to other species. 

 P. corotiata (Cda.), the common oat- 

 rust, and P. rubigo-vera, (D. C), 

 the barley-rust, are not infrequent on 

 grasses, the latter on the beautiful squirrel- 

 tail grass. They produce smaller clusters 

 of nredo-spores, and the cnshions of teleutosporea are long cov- 

 ered by the epidermis of the plant, and not so black. They are 

 also more frequent on the blade than on the sheath of the leaves. 

 P. magnusiana (Koern.), P. phragmitis (Schnm.), and P. amncli- 

 nacea (D. C), are found on the reed. These species all have 

 cluster-cups or aecidia on other species of plants. The rust 

 of corn is P. maydis (Carrad). The tall gramma grass is 

 infested by P. vexans {YavXow)', P. androp'jgi (Schw.), occurs 

 on broom-grass; P. nrundinariw {8chw.), on fall marsh grass; 

 and P. cynodontis (Desm.), on Bermuda grass. The common 

 rust of old witch-grass or tickle-grass is P. emaculata (Schw.) 

 etc. None of these species are known to produce cluster-cups. 

 4. €l0Yer-rust {Uromyccs trifolii, A. & S.) Producing mi- 

 nute white cluster-cups, pale brown uredo-pustules and darker 

 brown teleutospore-cushions, 1-64 in. in diameter, on the leaf- 

 stalks and blades of clover, especially white clover. 



Fia. Its:;.— a. Puccinto graminia oa wheat sheath; ib< P. ooroneta in oat leaf and c it* 



Bpores. 



