1910. | The Proteolytic Enzyme of Drosera. 137 
to indicate that apparently peptone is the ultimate product of the digestion 
of proteins by the digestive fluids of Drosera. It also shows that peptones 
are present in small amounts in the extract prepared from the leaves of 
the different species of Drosera, even in the ammonium sulphate precipitate, 
and that the amount is very rapidly increased if the extract is left at 
a fairly high temperature in contact with fibrin. 
This latter fact points to the existence of a pepsin-like enzyme which 
is apparently present in considerable quantities, and is not in the form of a 
zymogen. This latter statement agrees with that of Vines, who in his 
previously mentioned paper on the proteolytic enzymes of Nepenthes, came 
to the conclusion that the pitcher liquid of Nepenthes contains no zymogen. 
As the digestive process does not appear to extend beyond the production 
of peptones, it seems as if no traces of other proteolytic enzymes such as 
erepsin or trypsin are present; this does not altogether coincide with the 
results obtained by Vines in his researches on the pitcher liquid of 
Nepenthes. 
In accordance with his results, | have made very many attempts to find 
even the minutest signs of protein digestion carried to the amide stage, but 
have always been unsuccessful. I have been therefore forced to the conclusion 
of the non-production of these bodies in the species of Drosera mentioned, when 
growing under their normal conditions in the Victorian bush. It is in fact 
hardly to be expected that all carnivorous plants should carry out their 
digestion in exactly the same way and by the same means. 
In order to ascertain whether the leaves were capable of absorbing peptones, 
I performed the following simple experiment. 
A saturated peptone solution was prepared with carefully sterilised water, 
and after filtering it, two drops of the clear solution were applied to five 
similar marked leaves (which were apparently perfectly horizontal) of plants 
of Drosera Whittakert which were growing in a flower-pot. One of these 
leaves was cut off at once, and alsoa similar leaf to which no peptone solution 
had been added. The pot was now covered over with a large bell jar, the air 
inside which was kept damp. 
After leaving the flower-pot undisturbed for five hours the marked leaves 
were cut off and put into sterilised water and the biuret test applied. But 
in no case was any peptone reaction discernible, thus showing that, while all 
the water from the solution placed on the leaves had not completely 
disappeared, the peptone dissolved in the solution had done so, having been 
absorbed by the leaves of the plant. | 
Careful microscopic examination was made of the leaves after being 
cleaned, and also of those in which the remains of the insects’ bodies were still 
