MILDEWS, RUSTS AND SMUTS 69 
spores were seen to produce a promycelium, bearing promy¬ 
celium spores. 
MILESIA 
The only known species is parasitic on the fronds of ferns. 
The sori are small and yellowish, a.nd might be overlooked, 
except for their irregular disposition, for the sori of the fern. 
PUCCINIA 
The greatest variety of spore forms are met with in this 
genus. The aecidium or " cluster-cup ” stage is often pre¬ 
sent. The peridium or wart enclosing the spores is short, 
not reaching much above the level of the surface of the leaf 
through which it bursts. When mature the edge of the 
peridium is usually torn into irregularly triangular teeth, 
which curl outwards, exposing the golden mass of spores. 
This stage appears in the spring, and is followed in order 
by the uredo-and teleutospore forms, which appear on leaves 
or stems as small, scattered or crowded, minute warts or 
pustules, which burst through the epidermis and expose the 
spores. The sori or pustules of uredospores are usually 
brown, and those of the teleutospores blackish, and the 
spores are two-celled. 
GYMNOSPORANGIUM 
The aecidial condition is characterised by having an 
elongated, cylindrical, or horn-like peridium. All are 
produced on plants belonging to the order Rosaceae; 
pear, hawthorn, mountain-ash, etc. 
The teleutospores are parasitic on juniper branches, and 
cause swollen places, owing to the mycelium being perennial 
in the wood, and continuing to produce teleutospores year 
by year, over a gradually extending area of the host-plant. 
In old branches where the parasite has been present for some 
years, the swollen portions are usually more or less spindle- 
shaped, and may be a foot or more in length and three or 
four times the thickness of the normal part of the branch. 
During the spring these swollen portions become more or less 
thickly covered with dingy orange, subgelatinous masses of 
various forms, which ooze out through the bark. These 
masses consist of closely compacted teleutospores, which 
germinate in situ, the promycelium spores produced being 
dispersed by wind, infect the leaves of rosaceous plants, 
and give origin to the aecidium stage. 
So far as is known, both spore stages are absolutely 
necessary for the continuance of the species included in 
