Vines. — Proteolytic Enzymes in Plants. 263 
certainly yield a great deal of additional information. My 
observations on fruits indicate that the digestive activity, both 
peptonizing and proteolysing, is greatest when they are fully 
ripe, a condition that may be regarded as the first stage 
of decay. 
It would be premature at present to attempt any minute 
discussion of the physiological significance of the wide dis- 
tribution of a proteolytic enzyme in the body of the plant : it 
is obvious that what has hitherto been regarded as exceptional, 
must now be recognized as the rule, and this must profoundly 
affect many physiological conceptions. The most interesting 
point is that, in respect of their distribution, the proteases are 
now brought into line with the enzymes which are concerned 
with the carbohydrate metabolism of the plant. Just as 
diastase was, step by step, discovered to be everywhere 
present in the body of the plant, so now the same has been 
done for the proteolytic enzyme. No doubt the analogy 
also holds good with regard to their respective functions. 
Just as diastase facilitates the transference of temporarily 
deposited starch, so the proteolytic enzyme renders possible 
the distribution of the elaborated proteids. It is remarkable 
that this obvious analogy should not already have led to 
a search for a generally distributed proteolytic enzyme : but 
the difficulties in detecting and following the proteids in the 
tissues, difficulties which do not exist in the case of starch 
and sugar, are no doubt the sufficient reason. 
In conclusion, I may further point out that the case of 
‘ insectivorous ’ plants no longer stands alone. If leaves 
generally, or at any rate commonly, produce a proteolytic 
enzyme, it ceases to be remarkable that a similar enzyme 
should be formed by the leaves of certain of the ‘insecti- 
vorous * plants. The peculiarity of these plants is now limited 
to this — that their enzyme should be poured out at the 
surface, so that it digests proteids supplied from without by 
the captured insects ; whereas in ordinary plants the enzyme 
is retained within the tissue to digest, and so to render 
mobile, the proteids that are formed there. 
