Infection Experiments with Various Uredinecc. 187 
germ-tube. In the first place it is clear that entrance of the 
stoma by any germ-tube is no index of the capacity of that germ- 
tube to infect the leaf. If we may generalise from the cases 
given above, the germ-tubes of the spores of any member of the 
Uredineae may enter any leaf and grow there to some extent, while 
it is well-known that the capacity for infection of the spores of any 
one species is strictly limited. 
What causes the entry of the germ-tubes is at present unknown 
to us; probably as Miyoshi and others have supposed, it is the 
attraction of some substance to which the germ-tube is positively 
chemotropic, but far from its being a special substance for each 
plant, the evidence suggests that it is some substance common to 
all plants. We do not even know if it is liquid or gaseous; it seems 
possible it may be the latter, the stomata and inter-cellular spaces 
being emphatically an apparatus for gaseous inter-change. 
The second point to notice is that, it is the power of the hyphae 
to form haustoria, which we must take as an index of infective 
capacity ; because, if the fungus cannot use the host-plant as food, 
it must shortly die of starvation. Whether the incapacity to 
penetrate the cells is due to lack of attractive substance or to the 
presence of anything actively repellent is not clear, though as 
before stated, certain facts seem to suggest the presence of some¬ 
thing harmful to the hyphae. 
I will now proceed to certain results obtained in the course of 
a series of experiments on Chrysanthemum-rust. 
This rust exists the whole year through in the uredo-stage. 
Certain observers have reported the discovery of teleutospores in 
the months of December and January. It is impossible to con¬ 
tradict this statement, because the rust on individual plants may 
vary in this respect, but the occurrence of teleutospores is not 
general, for out of multitudes of spores, gathered from a collection 
of some hundreds of plants on many occasions from October to 
March, I have never found any teleutospores, nor have I found any 
in the pustules on my own plants which I have examined from time 
to time for the purpose. 
And indeed there is no necessity for resting spores, for the 
young shoots are above ground long before the old ones die away, 
and these young shoots are taken as cuttings, so that there is no 
time when there are no leaves upon which the rust can live. 
The time of year when there is an apparent break in the life of 
the fungus is from May to September. In fact so impressed was I 
by the disappearance of the rust in summer and its re-appearance 
