SECT. m. * . BUNT. 281 



through the stomates to the surface. Professor Henslow 

 has proved that the rust which appears on the leaves 

 and chaff scales of wheat is owing to the Uredo linearis, 

 a secondary form of the Puccinia Grarninis, and that rust 

 is only an earlier form of mildew ; so that the Puccinia 

 Graminis is a dimorphous and epiphytic fungus. It may 

 be a question whether the Uredo segetum, which destroys 

 the blossom of wheat, and reduces the ear to the sooty 

 mass of powder called smut, may not be the form of 

 some other fungus. The epiphytes of the order Puc- 

 ciniaei often appear on the exterior of plants in tuffcs of 

 brown, yellow, orange-coloured, or white sporangia. 



Fungi are extensively propagated by fragments of 

 their spawn, and the threads of the mycelia are some- 

 times diminished in thickness in order that they may 

 more easily penetrate into the stomates of the plant 

 they invade. -This was discovered by Mr. Berkeley 

 while investigating the germination of the spores of 

 bunt,, a foetid rust which attacks wheat and other 

 grasses. It is perfectly analogous to the diminution of 

 the size of the dust spores in the successive orders of 

 fructification. It is thought probable that in many of the 

 parasitic fungi, new spores are formed at the tips of the 

 fructiferous threads of the mycelium as fast as the ripe 

 spores fall off, whence that enormous mass of minute 

 spores which a single individual is capable of producing. 



Among the multitudes of known parasitic fungi, there 

 is not one that does not form a mycelium more or less 

 distinct. They do not arise from a disease in the plant 

 they attack, though they ultimately cause disease and 

 often death. Each parasite has its own mode of pene- 

 trating into the tissues, and its own manner of vege- 

 tating; they attack certain plants, and avoid others 

 though nearly allied. 



Dust spores, single or septate, oozing out of a dark or 

 coloured fungous mass is characteristic of the group 



