.MILDEWS, RUSTS AND SMUTS 
6i 
because one spore form grows on a buttercup, that the 
second spore form should grow on another kind of butter¬ 
cup, in fact just the opposite is usually the case, the two 
spore forms being parasitic upon host-plants that are 
widely separated from each other, from the standpoint 
of ainnity or relationship, as botanically understood. 
For instance, take wheat rust —Puccinia graminis ; the 
aecidium stage is parasitic on the leaves of the common 
barberry [Berberis vulgaris), a plant belonging to one of 
the two primary divisions of flowering plants, known as 
Dicotyledons, whereas the uredo- and teleutospore stages 
of the same fungus are parasitic on wheat and other grasses, 
which are included in the second great group of flowering 
plants, known as Monocotyledons. 
For the purpose of gaining experience in infection ex¬ 
periments, it will perhaps be best to commence with those 
species where the two different host-plants are known. 
This, of course, will depend on infected plants occurring in 
the neighbourhood where the would-be experimenter is 
residing. Numerous species of Puccinia are mentioned in 
the systematic portion following, whose host-plants are 
fairly common everywhere. Now suppose an aecidium is 
met with that is not known to be connected with any other 
spore form, and it is determined to experiment with it ; 
as already stated, there is no rule as to what other plant is 
likely to be its second host, providing it has one, conse¬ 
quently one or more kinds of vigorously growing plants, 
in the neighbourhood of the plant-bearing aecidia, should 
be infected. This is accomplished by depositing a few 
mature aecidiospores on a damp place on the leaf to be in¬ 
fected. If the infection proves successful, uredospores or 
teleutospores should appear at the points infected. When 
this result is obtained, it cannot be considered as completely 
proving that the fungus under consideration, grows on the 
two host-plants respectively. What remains to be done is 
to infect the plant bearing the aecidium with the spores 
produced on the plant infected with the aecidium spores, 
and if the aecidium stage results, it may then be safely 
assumed that the fungus in question has two spore forms 
produced on the two host-plants experimented upon. 
In the case of teleutospores that orf y germinate after 
a period of rest, that is, the spring following their production, 
it is advisable to keep the plants bearing the teleutospores, 
throughout the winter, under what may be termed natural 
conditions, that is, they should be placed in the open. 
