1 86 Vines . — The Proteases of Plants (///). 
of little use to the plant. The significance of the proteases in the economy 
is that they facilitate the translocation of organic nitrogen in the form 
of readily diffusible substances. This end is fully attained when the pro- 
teolysis is such as to produce from indiffusible proteids bodies like leudn, 
tyrosin, &c., but only imperfectly when it goes no further than the 
formation of albumoses and peptones. These facts and considerations also 
supply the material for an answer to Martin’s question on p. 173, and, it 
may be added, are as applicable in the case of animals as in that of 
plants. 
The duality of the enzymes is the main point to be determined, but 
it is by no means the only point : the wide differences in reaction-range 
both of peptolysis and of fibrin-digestion exhibited by the various juices 
and extracts have yet to be considered. How is the fact to be accounted 
for that peptolysis is retarded in the case of papain, Pineapple juice, and 
Nepenthes - liquid by a degree of alkalinity that in the other cases has little 
or no effect ; or the fact that fibrin-digestion is practically limited to acid 
reaction in the case of Nepenthes , Yeast, Mushroom, and Malt, whilst it 
is actively carried on in alkaline liquid by papain, Pineapple juice, and 
extract of Hyacinth-bulb? A possible explanation would be that the 
proteases are not of the same kind in the two sets of cases. On the 
hypothesis of a single c tryptic ’ protease it might be supposed that there 
exist several varieties of the protease. Similarly on the hypothesis of two 
proteases, an ereptase and a peptase, it might be supposed that varieties 
of ereptases and peptases exist in the different plants. But this is not the 
only possible explanation : another may be suggested, based not upon 
qualitative but on quantitative differences. I have found, in previous 
experiments with Yeast ( 4 ), that differences in the zymotic strength of an 
extract are accompanied by differences in its reaction-range: that, for 
instance, a degree of alkalinity that sufficed to inhibit fibrin-digestion by 
a 5% Yeast-liquid had little or no effect upon a io°/ o liquid. Quantity is 
therefore a factor in the problem : but, in view of the foregoing experi- 
mental results, the quantitative explanation is only applicable on the 
hypothesis of two proteases. Although the available facts are perhaps 
insufficient to settle finally the question as between the qualitative and 
the quantitative explanations — for these researches do not amount to more 
than pioneer-work— yet in some respects they distinctly support the latter. 
Thus the peptolytic results are on the whole so uniform, with a common 
range extending from distinct alkalinity to distinct acidity, that— if allow- 
ance be made for the incidental differences in the chemical composition 
of the various juices and extracts — there is no sufficient reason for 
attributing the observed differences in reaction-range to a distinct ereptase 
in each case. These differences may be more reasonably ascribed to 
variations in the quantity of one and the same ereptase : the reaction-range 
