i 18 William Brown. 
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 liverworts. These considerations 
point to the desirability of a more complete study of the hemi-,. 
cellulose (or pectin ?) series of cell wall constituents than has yet 
been attempted. 
General Conclusions on the nature of the Fungal Extract. 
At this stage it will add to clearness to summarise the main 
results obtained. 
The action of the fungus oilplant tissue maybe studied on the basis 
of the action of the extract employed. The macerating principle of the 
latter is of the natare of an enzyme and is a colloid of intermediate 
diffusive capacity. The lethal principle , if different from the former, 
is also colloidal, with a diffusive capacity at least as great as that of 
the enzyme. Crystalloids, and in particular, soluble oxalates play no 
part whatever in the lethal activities of the extract. 
II. Excretion of Active Principle by the Fungus. 
From the phenomenon of “ action in advance” already alluded 
to, it is clear that the active principle of the fungus is able to diffuse 
out of the fungal hypha into the plant tissue. An investigation was 
carried out with the object of determining to what degree the fungus 
was able to excrete its active principle into the culture medium. 
The results of this investigation are chiefly of technical and 
enzymological interest, and as they are of subsidiary importance in 
the progress of the investigation except in so far as they serve to 
indicate how the various contradictory statements on the subject 
have arisen, they will merely be referred to here. The amount of 
enzyme present in the culture fluid was found to increase up to 
about the time at which active growth of the hyphae ceased, that is^ 
to the time at which “ staling ” of the culture was reached, after 
which, the concentration continuously diminished. The nature of 
the preparation obtained was found to depend also upon the density 
of sowing and on the nature of the nutrient fluid. Some of the 
preparations obtained in this way are of a very active nature and 
contain much higher concentrations of enzyme than the standard 
extract previously employed. They are, however, less suitable for 
such a study as that described in Section I of this paper on account 
