Brown.—Studies in the Physiology of Parasitism. /. 347 
pronounced action on the pectin constituents of the cell-wall, and more 
especially on the so-called calcium pectate of the middle lamella. 
Whichever hypothesis be accepted as explaining the lethal action of 
the fungal extract, it is clear in any case that the chemical nature of the 
cell-wall is of fundamental importance in relation to the action of the 
fungal extract upon the cell. In all cases it has been found that if the cell- 
wall is disintegrated death of the cell ensues; if the cell-wall is not affected 
neither are the living contents of the cell. In other words, the nature of the 
cell-wall affords the key to the resistance of the particular tissue to the 
action of the fungal extract and therefore also of the fungus. In particular, 
certain experiments lead to the conclusion that there are important 
chemical differences between the cell-walls of higher plants and those of 
lower forms such as Hepaticae. These considerations point to the desirability 
of a more complete study of the hemicellulose (or pectin ?) series of cell-wall 
constituents than has yet been attempted. 
This investigation was undertaken at the suggestion of Professor V. H. 
Blackman, and has been prosecuted throughout under his guidance. It is 
with great pleasure that I take this opportunity of recording my indebted¬ 
ness to him for many helpful suggestions and for his continued interest. 
I. Summary. 
1. A method of preparing a very powerful extract from the germ tubes 
of Botrytis cinerea is described (Sections C and E, a). 
2 . The action of the extract on plant tissue is twofold : 
(a) Action on the cell-wall, leading to disintegration of the tissue. 
(b) Action on the protoplast, producing death (Section E, b). 
3. From microscopical investigation, death of the cells is seen to take 
place at a late phase of the process of disorganization of the cell-wall 
(Section E, b). 
4. The extract may be deactivated by heating, by mechanical agitation, 
and by neutralization with alkali. Deactivation by any method leads also 
to the loss of the lethal power of the extract (Sections F and G). 
5. Neither oxalic acid nor oxalates play any part in the toxicity of the 
extract. If any special lethal substance is present it must be of colloidal 
nature (Section F). 
6. The only active substance in the extract appears to be the enzyme, 
which produces a macerating action mainly by solution of the middle 
lamella. The enzyme appears also to be responsible for the lethal action 
of the extract, the death of the cells being brought about either by direct 
action of the enzyme on the protoplastic membrane, or indirectly as a result 
of the action upon the cell-walls (Section H). 
7. The ability of certain tissues to resist the action of the extract is 
dependent upon the special properties of their cell-walls (Sections E and G). 
A a 2 
