Brown.—-Studies in the Physiology of Parasitism. I. 315 
differences appear, though less prominently—the boiled liquid has here 
a relatively greater effect.’ 
Marshall Ward ( 2 ), in his treatment of this problem, made flask cultures 
of Botrytis on prune juice. After the lapse of three weeks, he removed the 
superficial weft of mycelium, which was then washed, dried, ground to 
a powder, and extracted in water. He was able to confirm de Bary as 
regards the presence of a cell-wall dissolving enzyme ; as regards the toxic 
nature of the extract he was unable to make any advance. 
Precisely similar results had been obtained a short time previously by 
Kissling ( 3 ), the same type of method being employed. 
Nordhausen ( 4 ) strongly emphasized the twofold aspect of the pheno¬ 
menon, enzymic and toxic. The following represents his conclusions : the 
active substances are ‘ apparently in part likewise enzymes, a conclusion 
which I reach from experiments similar to those of de Bary, although it 
is not excluded that oxalic acid under certain circumstances plays a part. 
That the latter, however, is not alone responsible for the toxic action 
on plant tissue is shown by the case of Aspergillus niger, which secretes 
oxalic acid in large quantities, even more so than Botrytis , without showing 
in any similar degree the marked parasitism of the latter.’ 
Behrens ( 5 ) used the expressed juice of fruits which had been infected 
with certain Fungi; thus in one case that of a pear infected with Mucor 
stolonifer , in another that of an apple infected with Penicillium luteum. In 
the latter case he mentions that the culture was allowed to develop for three 
months before the extract was investigated. These juices he found to be 
toxic to the mesocarp cells of Symphoricarpus berries, nor were the toxic 
effects reduced by boiling. Hence he concluded that the toxic substance 
was neither of volatile nor of enzymatic nature. 
Smith (6) compared the actions of weak oxalic acid solutions (o-oi 
per cent, to 1 per cent.) and of a mycelial extract of Botrytis on certain 
plant tissues (stem of lettuce), and while noting that the effects were not 
similar in all particulars—especially in respect of the post-mortem reactions 
induced—he concluded that oxalic acid, even in the lowest concentrations 
employed, was sufficient to produce the changes observed. He even goes 
so far as to state, on the basis of certain maceration effects of the acid, that 
the cell-wall dissolving effects of the fungus may be set down to this acid, 
quoting from de Bary that so much as 0-3 per cent, oxalic acid may occur 
in mycelial extracts. This author thus occupies an extreme position among 
those who ascribe an agency in this question to oxalic acid. 
As papers cognate to this subject may be cited those of Jones ( 7 ), 
Potter (8), and Van Hall ( 9 ). These investigations refer to bacterial plant 
diseases, and in each case it was shown that a cell-wall dissolving ferment 
could be obtained from media in which the organisms had been cultivated. 
This ferment is no doubt very similar to the Botrytis ferment under 
