Brown. — Studies in the Physiology of Parasitism. IV. 497 
General Remarks on the Secretion of Cytase by Botrytis 
cinerea . 
In the case of the watery extracts of mycelium it has been shown that 
a weak enzymic preparation is obtainable from the mycelial film in the case 
where the spores were sown thinly, while in the case of the dense sowings 
on glass plates a much stronger extract is obtained. Now the outstanding 
difference between the two cases mentioned is that in the latter case the 
great proportion of the hyphal mass is in a state of vigorous growth, or, at 
any rate, has very recently passed through its growth period ; whereas in the 
former, though the number of growing tips may be considerable, a large 
proportion of the fungal mass has ceased to grow. The small amount of 
enzyme obtainable in the latter case, as compared with the former, indicates 
that the source of enzyme is the growing region of the hypha. The older 
parts of the hypha do not contribute an appreciable amount of enzyme, 
but would probably tend to reduce by adsorption the amount going into 
solution during the process of extraction. 
This view, that enzymic formation is confined to the growing apex, is 
further supported by the results obtained in extracting hyphae which have 
ceased growing. In the glass plate experiments it was found that there 
was a marked diminution in the amount of enzyme obtainable from plate 
sowings of four and six days’ age as compared with that from plates one to 
two days old. As the plates were identical at the commencement, the older 
cultures must possess at least as many hyphal tips as the younger ones. 
The dry weight measurements show, however, that active growth ceases 
from about the second day. The reduced activity of the older cultures 
is thus to be set down in this case, not to a reduced number of hyphal tips 
in the extracted mass, but to reduction in the amount of enzyme in each 
hyphal tip, this reduction being correlated with the fact that these hyphal 
tips have ceased growth on account of the development of stale conditions 
in the culture. 
The elaboration of cytase in the fungal hypha would thus appear to be 
a process bound up with the protoplasmic activity associated with growth 
in the hyphal tip. Whether this enzyme plays a direct part in the changes 
undergone by the cell wall during the period of growth it is as yet im- 
possible to say. Again, the cause of the disappearance of this enzyme, 
both from parts of the hyphae which have ceased to grow and also from 
the medium in which growth has taken place, is not clear. It is known 
that its solution in water is not stable, and thus the disappearance of 
enzyme from cultures as time goes on may be due simply to this fact, 
though a process of actual resorption by the fungus is not impossible. 
