INJURIES INDUCED BY PLANTS 155 



On this account it will be necessary, as in the case of the 

 Ascomycetes, to append a list of imperfectly known rust-fungi, 

 to which, depending on the development form, the provisional 

 names of ALcidium, Cceoma, and Uredo are given. 



The rust-fungi are divided into several families, of which we 

 are here interested only in the Puccinia and Melampsorecz. The 

 former are characterised by the teleutospores being situated 

 singly, or several together on a stalk ; whereas, in the case of 

 the latter, the teleutospores are united to each other in large 

 numbers to form a firm palisade-like layer. 



PUCCINIA 



The genus Puccinia, which is rich in species, is characterised 

 by the teleutospores containing two cells and remaining attached 

 to the basidia, which at the same time serve as the stalk. They 

 appear as small brown or black brown heaps of a round or 

 oblong shape. 



Puccinia graminis * is the commonest kind of rust amongst 

 cereals, occurring everywhere, not only on our various kinds of 

 grain but also on many grasses. The teleutospores, which are 

 disposed in narrow ridges, hibernate on the common grasses, 

 though, if they have been produced on the lower parts of the 

 stems of cereals, they may also be left on the stubble fields. In 

 spring, when the sporidia that originate on the promycelia gain 

 a footing on the young leaves of the barberry, Berberis vulgaris, 

 they produce the barberry fungus, sEcidium Berberidis. The 

 aecidium form whose spores germinate on cereals and other 

 species of grasses, and produce the wheat- rust, Uredo linearis 

 is distinguished from the black ridges of teleutospores of 

 Puccinia graminis, which occur later, by the reddish brown 

 colour. 



This destructive cereal rust may be most effectively combated 

 by rooting out the barberry. This measure must not, however, 

 be confined within narrow limits, because the spores of the bar- 

 berry-fungus can be widely distributed by wind. 



*'[This, the common rust of wheat and other grasses, is of classical 

 interest, since it was this species in which De Bary first established the 

 remarkable phenomenon of heteroecism. ED.] 



