THE FUNGI 263 



few years later by the independent experiments of a 

 Danish schoolmaster named Schoeler. Botanists, however, 

 were still unwilling to accept the fact, because the 

 Puccinia of the wheat had quite different characters 

 from the dBcidium of the Barberry. It was not till 

 1865 that the complete demonstration of all stages of 

 the life-history of the parasite was accomplished by the 

 German botanist De Bary. Now we know of a great 

 many other cases of heteroecism among allied Fungi. 



We must not suppose, however, that the change of 

 host is absolutely necessary for the perpetuation of a 

 heteroecious parasite such as Puccinia graminis. In 

 Australia, for example, rust is prevalent on Wheat to a 

 serious extent, though there are no Barberry bushes nor 

 any other plant on which the ^Ecidium form has been 

 observed. In parts of England also the disease is well 

 known, though there is no Barberry in the neighbour- 

 hood. In such cases it is evident that the Uredo form 

 must persist through the winter, probably on wild 

 grasses growing as weeds on the cornlands, the uredo- 

 spores infecting the new crop in the following spring. 

 Under such conditions, the teleutospores are useless, for 

 their sporidia can only infect the other host, and not 

 the Grammes. In the absence of the Barberry the 

 Fungus produces a very large proportion of uredospores 

 in comparison with teleutospores, no doubt because those 

 individuals which are most prolific in the former have 

 had the best chance of perpetuating their race. 



Some other members of the Uredincce have a very 

 simple life-history compared with Puccinia graminis. In 

 many of them all stages of the Fungus are passed through 

 on the same host-plant, while in others certain of the 

 stages are missing altogether. 



