MILDEWS, RUSTS AND SMUTS 
55 
properly called aecidiospores, are usually globose or subglo- 
bose, with a colourless wall, which is generally ornamented 
with minute warts or spines, and is also furnished with thin 
places or germ-pores, through which the germ-tubes emerge 
on germination. When quite fresh, aecidiospores germinate 
freely in water, and the process can readily be studied in a. 
hanging-drop. In the majority of species the aecidia are 
cup-shaped, and do not proj,ect much above the surface 
on which they are growing. Such forms were at one time 
considered as independent species, and were included in a 
genus called Aecidium. Other aecidia are considerably 
elongated, and cylindrical or horn-shaped,- with a torn 
fringed opening at the tip when mature. Such forms once 
constituted the genera Peridermium and Roestelia. In 
other aecidia again, the peridium is almost or quite absent, 
but in such instances the presence of the spores originating 
in chains indicates their nature. On germination, aecidi¬ 
ospores produce one or more germ-tubes, which become 
branched and form mycelium directly. 
Where several different forms of fruit enter into the life- 
cycle of a species, as previously stated, the aecidium stage 
appears first, and its spores infect the same, or some dif¬ 
ferent kind of host-plant, the mycelium of which gives 
origin to the next fruiting stage, as uredospores or teleuto- 
spores. In some instances, however, several generations 
of aecidia may follow each other, resulting from infection 
by aecidiospores, before the next form in the cycle of develop¬ 
ment is produced, as in Puccinia senecionis, Lib. Aecidia 
that are the result of the germination of teleutospores— 
the most general method, have been called primary aecidia, 
whereas aecidia that result from the germination of aecidios¬ 
pores are known as secondary aecidia, 
Uredospores 
When the cycle of forms in a fungus is complete, the 
uredospore stage follows the aecidium condition, resulting 
from infection by aecidiospores. Uredospores are produced 
in crowded heaps called sori (sing, sorus), which originate 
under the epidermis of the host-plant. When the spores 
are mature the epidermis is ruptured and the spores are 
exposed, and readily dispersed by wind, etc. In some 
species the sori are circular, in others elongated, and are 
usually more or less rusty or brown in colour. Uredospores 
consist of one cell, and are produced singly at the tips of 
slender hyphae, and are usually more or less globose, with 
