Studies in the Physiology of Parasitism. 1 
I. The Action of Botrytis cinerea. 
BY 
WILLIAM BROWN, M.A., B.Sc. 
Contents. 
PAGE 
A. Introduction.313 
B. Historical.314 
C. Preparation of ‘Standard Ex¬ 
tract’ .318 
D. Quantitative Method of study¬ 
ing Action of Extract . . . 324 
E. Action of Extract on Tissues: 
(a) General Account . . . 328 
( 3 ) Detailed Account of cer¬ 
tain Cases.332 
F. Examination of certain Physical 
Relationships of Extract. Re¬ 
page 
lation to Heating, Mechani¬ 
cal Agitation, Diffusion, and 
Dialysis.335 
G. Relation of Activity to certain 
Chemical Substances. Effect 
of varying Acidity, of Salts, 
of Non-electrolytes, of Plant 
Juices, &c . 33 s 
H. Discussion of the Nature of the 
‘Lethal Principle’ of the 
Extract.345 
I. Summary.347 
A. Introduction. 
T HE physiological relation of host and parasite is a subject urgently in 
need of investigation at the present time. On a knowledge of such 
relations must depend any further insight into the nature of immunity and 
susceptibility of plants to disease. In the case of the more highly specialized 
parasites there is considerable difficulty in studying their physiological 
relations to their host owing to the complexity of the relationship, which 
often amounts almost to symbiosis, and to the difficulty of growing the 
parasites independently and of bringing about infection at all times of 
the year. It seemed probable, then, that a closer investigation, by modern 
biochemical methods, of the mode of action and method of infection of some 
of the simpler parasites which can be easily cultivated would be of great 
value. A knowledge of the relationship of such forms to their hosts 
should lead the way to a better understanding of the more highly specialized 
parasites. It was with this view that the present investigation was under¬ 
taken. 
1 This is the first of a series of studies which are being carried out in the department of Plant 
Physiology and Pathology of the Imperial College of Science and Technology. 
[Annals of Botany, Vol. XXIX. No. CXV. July, 1915.] 
Y 
