of the tentacles bearing these glands were inflected, and remained so
for the two succeeding days, when they appeared dead.]
Concluding Remarks on the Action of Acids. It is evident that acids
have a strong tendency to cause the inflection of the tentacles;* for
out of the twenty-four acids tried, nineteen thus acted, either rapidly
and energetically, or slowly and slightly. This fact is remarkable, as
the juices of many plants contain more acid, judging by the taste, than
the solutions employed in my experiments. From the powerful effects of
so many acids on Drosera, we are led to infer that those naturally
contained in the tissues of this plant, as well as of others, must play
some important part in their economy. Of the five cases in which acids
did not cause the tentacles to be inflected, one is doubtful; for uric
acid did act slightly, and caused a copious secretion of mucus. Mere
sourness to the taste is no
* According to M. Fournier ( De la Fcondation dans les Phanrogames.
1863, p. 61) drops of acetic, hydrocyanic, and sulphuric acid cause the
stamens of Berberis instantly to close; though drops of water have no
such power, which latter statement I can confirm; [page 197]
criterion of the power of an acid on Drosera, as citric and tartaric
acids are very sour, yet do not excite inflection. It is remarkable how
acids differ in their power. Thus, hydrochloric acid acts far less
powerfully than hydriodic and many other acids of the same strength,
and is not poisonous. This is an interesting fact, as hydrochloric acid
plays so important a part in the digestive process of animals. Formic
acid induces very slight inflection, and is not poisonous; whereas its
ally, acetic acid, acts rapidly and powerfully, and is poisonous. Malic
acid acts slightly, whereas citric and tartaric acids produce no
effect. Lactic acid is poisonous, and is remarkable from inducing
inflection only after a considerable interval of time. Nothing
surprised me more than that a solution of benzoic acid, so weak as to
be hardly acidulous to the taste, should act with great rapidity and be
highly poisonous; for I am informed that it produces no marked effect
on the animal economy. It may be seen, by looking down the list at the
head of this discussion, that most of the acids are poisonous, often
highly so. Diluted acids are known to induce negative osmose,* and the
poisonous action of so many acids on Drosera is, perhaps, connected
178