442 
Pole Evans . — The Cereal Rusts. 
histology, physiology, and ecology of these Fungi has now been obtained, 
in addition to many interesting facts connected with the relative immunity 
of the various hosts. 
The development of the Uredo mycelium of the Fungi (to be described) 
has been followed in detail from the time of spore-germination to spore- 
production. In such a course of development we have to recognize three 
distinct stages - 
1. The attack by the parasite on its host, or the first phenomenon 
of occupation. 
2. The course taken after occupation by the further growth of the 
parasite. 
3. The reaction on the host after occupation and the subsequent 
reciprocal action of host and parasite. 
It is mainly to the attack by the parasite on its host, or the first 
phenomenon of occupation, that we shall confine our attention in this paper. 
Up to the present the complete series of these rusts has not been 
obtained, but as I have examined all the species which are known to occur 
on Cereals, it is thought advisable to publish them without further delay, 
and leave several species which occur on the more uncommon grasses 
for a future investigation, should they be obtained. 
A detailed histological study has also been made of the so-called 
{ physiological species,’ ‘ biologic species,’ ‘ sister species,’ or ; specialized 
forms’ of rusts, and points of great interest have come to light. These 
I hope to publish at an early date. 
Methods. 
The methods adopted for studying the histology are as follows : — 
1. Selection of host plants. For infection purposes, seedlings of plants 
known to be susceptible to the particular kind of rust which it was desired 
to study were raised. In most cases, directly the first foliage leaf was fully 
expanded, a series of inoculations were made by laying the spores on the 
inner face of the leaves with a flat platinum needle. Sowings of spores 
were also made at the same time in watch glasses of distilled water as 
control experiments to observe the germination capacity of the spores. 
2. After inoculation damp bell-jars were placed over the plants 
for forty-eight hours. 
3. The inoculated portions of the leaves were then removed and fixed 
daily until the crop of uredo-pustules made their appearance. As a rule 
this generally took place about the tenth day, but was liable to considerable 
variation, according to the different rusts under investigation. 
In this way the life-history of the Fungus was studied from the period 
of germination of the spore up to the time that it had successfully repro- 
duced itself on its particular host. 
