95 



the cultivated Hollyhock. The fungus, which is a native 

 of Chile, was introduced into Europe about 1875, and for 

 some years its ravages were so severe that it was scarcely 

 possible to grow the Hollyhock free from rust. Even at 

 present the disease causes considerable trouble in some 

 districts. 



The disease pustules chiefly occur on the leaves, but the 

 stem and even the flower buds and fruits are often 

 attacked. As in the rusts already described, the develop- 

 ing cushion of spores bursts through the epidermis. The 

 filaments of the fungus ramify in the tissues of the host 

 sending haustoria into the living cells, which are slowly 

 depleted of nutritive substances. The pustules arise on 

 both surfaces of the leaf, are small and circular in out- 

 line and produce teleutospores only. These germinate 

 in situ under suitable conditions, immediately they 

 mature, giving rise to sporidia as in other rusts. The 

 sporidia, falling on to the surface of any part of a 

 hollyhock plant germinate and penetrate the epidermis 

 producing an infection. From this region a new pustule 

 of teleutospores is produced in about fourteen days. The 

 Hollyhock rust thus omits both the aecidiospore and 

 uredospore stages from its life story. 



The fungus probably passes the winter by teleuto- 

 spores which fail to germinate owing to unfavourable 

 conditions. In addition it is likely that it also is carried 

 over in the few radical leaves which generally survive the 

 winter in this country. The writer has frequently observed 

 incipient disease spots on such leaves in the winter, and 

 it is probable that these develop much more slowly in the 

 cold weather than those produced in the warmer months. 

 By destroying diseased leaves as soon as the spots appear, 

 it is usually possible to restrict the damage caused bv this 

 rust. 



From the examples described in this chapter it will be 

 evident that, although the fungi causing the rust diseases 

 belong to one group, yet they present certain differences 

 from one another. A large number, like the rust of wheat, 

 produce aecidiospores on one host, and the uredospores 

 and teleutospores on an entirely different species of plant. 

 Others, however, like the rust of mint pass the whole life 

 cycle on one host and give rise to aecidiospores, uredo- 

 spores and teleutospores in succession on the same species. 

 Still others like the Hollyhock rust, in addition to living 



