RUST FUNGI 20I 



times resulting in the death of the animals. Its urediniospores and 

 teliospores are on compositous plants and its aecial stage on the pitch 

 pine, Pinus rigida, this stage being known in the older books as 

 Peridermium acicolum. The species of the genus are all heteroecious, 

 and ascial stages, whenever found, occur on species of Pinus and 

 are referable to the form genus Peridermium. Arthur and Kern 

 enumerate twenty-seven species of Peridermium, ranging from Mexico 

 to Alaska, and from the Atlantic to the Pacific coasts. The species 

 are all secia of species belonging to tehal genera, but they cannot 

 be always satisfactorily assigned because of incomplete knowledge 

 regarding them. The genus Peridermium embraces all aecial forms 

 possessing peridia, inhabiting the Pinace^ and Gnetace^. Only 

 three of the twenty-seven American species have been associated with 

 telial forms as follows: 



Peridermium pini connected with Coleosporium campanulcc on 

 Campanula. 



Peridermium cerebrum connected with Cronartium on oak. 



Peridermium elatinum connected with Melampsorella cerastii. 



Family Pucciniace^. — In this family, the teliospores usually con- 

 sist of a single cell, or a vertical row of superimposed cells sometimes 

 united into a small bead-like cluster. The teliospores are borne on a 

 simple, or a compound pedicel. The urediniospores are single, on 

 hyaline, deciduous stalks. The secia usually have a peridium. The 

 most important genera of the family are: Uromyces, Puccinia, Gymno- 

 sporangium, Gymnoconia (Fig. 71) and Phragmidium. 



The rusts belonging to the genus Uromyces have one-celled winter, 

 or teliospores, which are egg-shaped, individually separated and massed 

 in small, open spore groups. The important pathologic species are the 

 clover rust, Uromyces trifolii; the rust of beans, U . appendiculata; beet 

 rust, U. betcB; carnation rust, U. caryophyllinus (Fig. 70). The largest 

 genus of the rusts, Puccinia, has usually two-celled teliospores, although 

 unicellular ones may occur in some species. The principal cereal or 

 grain rusts may be enumerated first, as they are fairly well known, 

 owing to the researches of Eriksson and others: 



Black Rust of Cereals, Puccinia graminis (Fig. 64) with its aecium 

 on the barberry, Berberis vulgaris. Six forms of this species may be 

 distinguished: (i) f. sp. h-itici on wheat (seldom on rye, barley 

 and oats); (2) f. sp. secalis on rye, barley and couch grass, Agropyron 



