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 
zz stfz 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 by this 
tust. 
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 Hollvhock rust, in addition to living 
