Cuar. VI] DIGESTION, 73 
moistened with water is slightly acid, I compared its action 
on litmus paper before it was placed on the leaves, and 
afterwards when bathed in the secretion; and there could 
not be the least doubt that the latter was very much more 
acid. I have indeed tried hundreds of times the state of the 
secretion on the discs of leaves which were inflected over 
various objects, and never failed to find it acid. We may, 
therefore, conclude that the secretion from unexcited leaves, 
though extremely viscid, is not acid or only slightly so, but 
that it becomes acid, or much more strongly so, after the 
tentacles have begun to bend over any inorganic or organic 
object; and still more strongly acid after the tentacles have 
remained for some time closely clasped over any object. 
I may here remind the reader that the secretion appears to 
be to a certain extent antiseptic, as it checks the appearance 
of mould and infusoria, thus preventing for a time the 
discoloration and decay of such substances as the white of an 
egg, cheese, &c. It therefore acts like the gastric juice of 
the higher animals, which is known to arrest putrefaction by 
destroying the microzymes. 
As I was anxious to learn what acid* the secretion contained, 445 
leaves were washed in distilled water, given me by Prof. Frankland ; 
but the secretion is so viscid that it is scarcely possible to scrape or 
wash off the whole. The conditions were also unfavourable, as it was 
late in the year and the leaves were small. Prof. Frankland with 
great kindness undertook to test the fluid thus collected. The leaves 
were excited by clean particles of glass placed on them 24 hrs. 
previously. No doubt much more acid would have been secreted had 
the leaves been excited by animal matter, but this would have rendered 
the analysis more difficult. Prof. Frankland informs me that the 
fluid contained no trace of hydrochloric, sulphuric, tartaric, oxalic, or 
formic acids. This having been ascertained, the remainder of the 
fluid was evaporated nearly to dryness, and acidified with sulphuric 
acid; it then evolved volatile acid vapour, which was condensed and 
Gorup 
* [Messrs Rees and Will (‘ Bot. 
Zeitung,’ 1875, p. 716) stimulated the 
glands of some thousand Drosera 
plants with glass-dust and analysed 
the secretion thus produced. They 
found a variety of fatty acids present, 
among which Formic acid was recog- 
nised with certainty, and Propionic 
and Butyric acids were suspected from 
the eyidence of the smell. 
and Will have shown that the neutral 
secretion of Nepenthes becomes power- 
fully digestive when acidulated with 
formic acid (see ‘ Bot. Zeitung,’ 1876, 
p- 476). It is therefore interesting 
to find this acid naturally present in 
the secretion of Drosera.—F.D.] 
