l8o PARASITIC FUNGI 



in a drop of rain or dew on the surfaces of fresh wheat 

 leaves, and the germ hyphae enter the stomata 

 (Fig. 19, B), branch within the leaf, and penetrate the 

 living cells. Hyphae from this mycelium burst out 

 from the surface of the leaf again, forming fresh masses 

 of uredospores ; and so the process is repeated, and 

 the fungus spreads during the latter part of the grow- 

 ing season from one wheat field to another. 



The uredospores formed about the time the crop is 

 harvested can survive the winter and are capable of 

 infecting the young wheat plants in the following 

 spring. But another kind of spore, the teleutospore* 

 two-celled and with thick dark walls (Fig. 19, C), are 

 also formed in numbers towards the end of the season 

 by the mycelium of Puccinia graminis (the Black 

 Rust). The teleutospore hibernates, and in the spring, 

 instead of germinating directly to form a new mycelium, 

 sends out short thin hyphae which cut off small thin 

 walled conidia called sporidia (Fig. 19, D), and these do 

 not infect the wheat plant, but instead the leaves of 

 the barberry (Berberis vulgar is), a not uncommon 

 shrub of hedgerows. The germ tubes from the sporidia 

 form mycelia within the barberry leaf, and these form 

 spores of a fourth kind (cecidiospores) in cup-shaped 

 structures (cecidia) on the surface of the leaf (Fig. 19, E) . 

 At the base of each cup-shaped structure there is a 

 mass of parallel hyphae at right angles to the surface 

 of the leaf, and from the end of each a chain of 

 aecidiospores is budded off in much the same way that 

 the conidia of Penicillium are budded off from the 

 end of the conidiophores (p. 164). These aecidiospores 

 are detached, and if they germinate on a wheat leaf 



1 Greek reAeur^, end, because they are formed at the end of the 

 season of active growth of the fungus. 



