in the Brontes and their Brown Rust . 301 
To sum up, then, I should place in the foreground the fact 
that three phases must be considered in infection : 
(1) The germination of the Uredospore. 
(2) The act of inoculation or infection ; and 
(3) The incubation period or growth of the mycelium in the 
tissues. 
Each of these phases has its vicissitudes. The germination 
depends on the vigour and previous nutrition of the spore, as 
well as on the factors of the environment active during the 
process ; and the nature and vigour of the resulting germ- tube 
are determined especially by these. 
The act of inoculation, or entry of the germ-tube into 
a stoma, brings into play new factors ; for the living cells 
attacked, with their known capacities for producing acids, 
enzymes, food-stuffs, chemotactic substances, &c., cannot be 
regarded as passive. It depends on these whether the germ- 
tube can gain a safe entrance. It may be so well adapted 
that this is easy, e. g., from B. mollis to B. mollis y or it may be 
that the over- energetic germ-tube destroys the guard-cells, &c., 
and so ruins the affair at the start, e. g., from B . mollis to 
B. sterilis . 
Once inside, the young mycelium is still by no means 
assured of successful development and growth. Even in a 
host-species naturally accommodating, e. g. B. mollis to the 
Fungus from B. mollis , a lack of minerals, especially potassium 
or phosphorus, may bring about slow starvation ; or the 
temperature may be too high for the Fungus, though the 
grass itself withstands it well ; or the host is so shaded 
that it assimilates badly and so forth. All these and similar 
events will have their effect, and the starved mycelium may 
die or lie dormant till the leaf dies, or possibly be resuscitated 
again if affairs improve before the life of the leaf is ended. 
It seems to me that many cases of delayed outbreak of 
the Fungus, of apparent failure of attack, of poorly developed 
pustules, and of feebly germinating spores are to be explained 
by the above considerations. 
When the invading germ-tube finds itself in the leaf of 
