On the Relations between Host and Parasite 
in the Bromes and their Brown Rust, 
Puccinia dispersa (Erikss.) 
BY 
H. MARSHALL WARD, D.Sc., F.R.S., 
Fellow of Sidney Sussex , Honorary Fellow of Christ's College, and Professor 
of Botany in the University of Cambridge. 
i. Introductory. 
S OME years ago I gave a summary of the factors and 
questions involved in the study of the relations between 
host and parasite in certain epidemic diseases of plants \ and 
have at various opportunities since then continued investiga- 
tions into that subject. In particular, I have for some time 
been occupied with researches planned with the object of 
ascertaining more concerning the modes of infection and 
attack of the Uredo-form of certain Rust-fungi. 
During the course of this work I had occasion to select 
a particular genus of grasses, viz. the Bromes — with the view 
of examining their anatomy and histology in detail, in refer- 
ence to the behaviour of the fungus in their tissues. In course 
of time a series of phenomena came to light which led me 
to go further into the conditions of infection, and to make 
numerous experiments with the Uredo of the Brown Rust — 
Puccinia dispersa — so common on certain species of this 
genus. These experiments led to some unexpected results, 
and the purpose of the present paper is to put together these 
1 Croonian Lecture, Proc. R. S., vol. 47, 1890, p. 393, 
[Annals of Botany, Vol. XVI. No. LXII. June, 1902.] 
R 
