Vines. — Proteolytic Enzymes in Plants. 259 
of oxidases and peroxidases in plants. I cannot presume to 
offer one now, as I have merely glanced at the subject. But 
I have observed a fact that seems to be worth recording and 
bears directly upon it : — it is that when I have found a liquid 
or a tissue to give a good reaction with guaiacum, whether 
with or without H 2 0 2 , I have also found it to be proteolytic ; 
whereas, when its guaiacum-reaction is wanting, it is deficient 
in proteolytic activity. For instance, having observed that 
neither the juice nor the pulp of the Orange gave any 
guaiacum-reaction, whilst the peel gave a strong peroxidase- 
reaction, I found the peel to be actively proteolytic but not 
the juice or the pulp (see p. 246). Exactly the same occurred 
in the case of the Apple (see p. 245). Again, the pulp of 
some white Spanish grapes slowly gave a faint peroxidase- 
reaction, and was found to have little proteolytic action on 
Witte-peptone: some fully-ripe English hot-house grapes, on 
the contrary, both white and black, gave the oxidase-reaction 
and digested Witte-peptone. 
The association of these oxidizing substances with enzymes 
may be only a coincidence, or it may indicate a relation 
between oxidative and enzymotic activity. It is one that has 
already attracted attention, for it was thought at one time 
that the enzymes themselves reacted with guaiacum. But 
this is not the case: papain, for instance, gives no reaction. 
Assuming, as seems more probable, that co-existence means 
correlation, it is not an impossible suggestion that oxidase or 
peroxidase may be concerned with the formation of the 
enzyme, whether protease, glucase, lipase, &c. : that, for 
instance, their oxidative action may determine the liberation 
of the enzyme from its zymogen. 
This suggestion may perhaps supply the true physiological 
interpretation of Raciborski’s ( 7 ) important observation that 
the sieve-tissue of plants gives the peroxidase-reaction, as 
also of the fact that the reaction is likewise given by latex. 
The latex of the Papaw and of the Fig is known to actively 
digest proteids ; and my observations on Euphorbia Characias 
and on the Lettuce (p. 247) indicate that this is true of 
