406 Brown . — Studies in the Physiology of Parasitism . III. 
the infection drops employed there was however no possibility of such high 
concentrations, either of acid or of salt. In the experiments in this connexion 
a glucose-peptone medium was employed. This medium contained a trace 
of a calcium salt (derived from the commercial peptone preparation), which 
in the medium as made up was determined by titration to be of strength 
71 71 
— .. Sowings were made in this medium in the usual way, and as 
800 1,000 J 
soon as discoloration was observed the drops were collected and cleared of 
spores by centrifuging. The addition of a drop of potassium oxalate 
to this liquid gave a distinct precipitate, thus showing that a soluble calcium 
salt was still present in the infection drop. It is plain therefore that the 
figure represents an upper limit to the amount of oxalate excreted by 
the fungus into the infection drop. The actual amount of oxalate formation, 
if any, is certainly much below this figure. Thus in plate sowings of two 
days’ age in which the same glucose-peptone medium was employed, the 
excretion of soluble oxalate had not gone so far as to precipitate all the 
calcium from solution. 
It appears therefore that the formation of soluble oxalate in young 
fresh cultures of Botrytis, if it take place at all, is negligible in amount, and 
that vigorous attack by the fungus can take place under conditions where 
the presence of a soluble oxalate is quite excluded. 
Conclusions. 
The infecting germ tubes of Botrytis cinerea are unable to affect 
chemically the cuticle of the host, nor do they secrete any toxic substance 
which can pass through the cuticle and bring about the death of the under- 
lying cells. The fungus is unable to affect the underlying tissue until the 
obstacle afforded by the cuticle has been overcome. Chemical action being 
excluded, penetration of the cuticle must take place in a purely mechanical 
way. Once penetration of the cuticle has been accomplished, the underlying 
tissue is attacked after the manner described in the first number of this 
series. 
The results of this purely physiological study are in exact agreement 
with the results of a microscopical study by Blackman and Welsford 1 of 
infection of the bean leaf by Botrytis cinerea. 
1 No. II of these studies. Ann. Bot., vol. xxx, 1916, p. 389. 
