314 Brown.—Studies in the Physiology of Parasitism, I. 
Botrytis cinerea is a member of the large physiological group of Fungi 
known as ‘Facultative Parasites 5 , the members of which while normally 
saprophytic are able under certain conditions to live parasitically. Among 
Fungi of this type, the subject of the present investigation is somewhat pre¬ 
eminent, partly on account of its ubiquity, partly by reason of the striking 
features of its parasitic attack. When to these is added the fact of its being 
very amenable to cultural treatment, it is not surprising that this form has 
become a classical one for the study of the physiological questions relative 
to this type of parasitism. As a result of these researches certain features 
of this type of parasitic activity may now be considered as being firmly 
established. Prominent among these is the one due to de Bary (1), and since 
his day frequently confirmed, that such Fungi possess the power of killing 
and disintegrating the tissues of the host in advance of .their growth, so that 
properly speaking they are not parasitic upon the living host at all, but live 
merely on its dead remains. This phenomenon of ‘ action in advance 5 
de Bary set down to the excretion by the tips of the advancing hyphae of 
some soluble substance which is capable of bringing about the observed 
changes—changes consisting, firstly, in the solution of the cell-wall, or 
at least of certain of its constituents, so that the tissue loses its coherence; 
and, secondly, in the killing of the living protoplasmic contents themselves. 
So far we find general agreement, but when we come to treat of the nature 
of this soluble substance, of what it consists, of how many chemical entities it 
consists, and what share in the process is assignable to each, we meet with 
considerable divergence of opinion. This will be made clear from a review 
of the literature dealing with this question. 
B. Historical. 
De Bary ( 1 ), in a paper now classical, investigated the parasitism 
of Sclerotinia Liber tiana^ a form closely allied morphologically to Botrytis 
cinerea , and showing many similarities in its mode of parasitism. By using 
the expressed juice of certain plant organs (roots of carrot, &c.) which had 
been infected and overrun by the fungus, as also the liquid exuded in 
droplets from the young sclerotia of the fungus itself, he was able to show 
that the active principle was thermolabile, and so concluded that it was 
of the nature of a ferment. The cell-wall dissolving activity of the fungus 
he unhesitatingly ascribed to this enzyme ; as to the toxic activity he was 
somewhat doubtful. He discussed the possibility of the latter being due to 
some soluble oxalate, and while showing that oxalates do occur in certain 
secretions of the fungus, he was unable on quantitative grounds to ascribe 
to these the markedly destructive effects of the fungus. His final con¬ 
clusions may be taken as summarized in the following quotation: ‘ The 
difference (between boiled and unboiled extract) is indeed a quantitative one 
as far as can be observed. . . . With the liquid from sclerotia the same 
