Notes. 
5^1 
allied B. maximus. Broadly speaking, the uredo-spores, growing 
on a species belonging to the Serrafalcus group, infect other members 
of that group— in varying degree, however, and not necessarily all — 
but fail to induce the development of pustules on species belonging 
to another group — e.g. Stenobrovius or Festucoides. 
There is evidence, however, going to show that an occasional 
adaptation to another species may occur in cases where infection does 
not usually succeed. In such cases, the Uredo having once established 
itself on another species, its uredo-spore progeny will thenceforth „ 
readily infect that species. 
The rule seems to be that the uredo-spores infect most easily the 
species and variety on which they have been developed, less easily 
varieties or species more remote, and fail altogether to gain a hold 
on more distant ones. 
This does not appear to be a matter depending merely on the 
structure of the leaves of the host plant, or on any recognizable 
excretion from them ; at any rate the microscope shows none such, 
and experiments with B. mollis and B. sterilis demonstrated that the 
germ-.tubes grow readily in filtered extracts, boiled or unboiled, of the 
leaves. The matter evidently depends on the influence of the previous 
nutrition of the Fungus, as well as on the reactions of the species 
attacked, and presents problems of great complexity. 
It is possible to grow pure cultures of the grass as well as of 
the Fungus for weeks and even months in closed and in aerated tubes. 
‘ Seeds/ sterilized by various reagents, have been germinated in 
large tubes, on cotton- wool supplied with pure nutritive materials, 
and excellent plants thus raised out of contact with any but filtered 
air. Such pure cultures have been infected with uredo-spores, and the 
progeny utilized for similar re-infections, thus ensuring pure cultures 
of both host and parasite. 
‘ Seeds/ from infected plants, thus treated do not give rise to 
infected plants ; and unless spores are sown on the leaves of the 
“latter no pustules are developed. Moreover, pustules only arise in 
these cases on the spots where fhe spores were sown, and within the 
usual incubation period. These facts seem to militate against any 
theory of internal seminal sources of disease. It is hoped that by 
longer series of such pure cultures more definite information on 
several obscure points will be obtained. 
At present the evidence points to the following conclusions. The 
