movement often through an angle of above 180o. I know not whether to be
most astonished at this fact, or that the pressure of a minute bit of
hair, supported by the dense secretion, should quickly cause
conspicuous movement. Moreover, this extreme sensitiveness, exceeding
that of the most delicate part of the human body, as well as the power
of transmitting various impulses from one part of the leaf to another,
have been acquired without the intervention of any nervous system.
As few plants are at present known to possess glands specially adapted
for absorption, it seemed worth while to try the effects on Drosera of
various other salts, besides those of ammonia, and of various acids.
Their action, as described in the eighth chapter, does not correspond
at all strictly with their chemical affinities, as inferred from the
classification commonly followed. The nature of the base is far more
influential than that of the acid; and this is known to hold good with
animals. For instance, nine salts of sodium all caused well-marked
inflection, and none of them were poisonous in small doses; whereas
seven of the nine corre- [page 273] sponding salts of potassium
produced no effect, two causing slight inflection. Small doses,
moreover, of some of the latter salts were poisonous. The salts of
sodium and potassium, when injected into the veins of animals, likewise
differ widely in their action. The so-called earthy salts produce
hardly any effect on Drosera. On the other hand, most of the metallic
salts cause rapid and strong inflection, and are highly poisonous; but
there are some odd exceptions to this rule; thus chloride of lead and
zinc, as well as two salts of barium, did not cause inflection, and
were not poisonous.
Most of the acids which were tried, though much diluted (one part to
437 of water), and given in small doses, acted powerfully on Drosera;
nineteen, out of the twenty-four, causing the tentacles to be more or
less inflected. Most of them, even the organic acids, are poisonous,
often highly so; and this is remarkable, as the juices of so many
plants contain acids. Benzoic acid, which is innocuous to animals,
seems to be as poisonous to Drosera as hydrocyanic. On the other hand,
hydrochloric acid is not poisonous either to animals or to Drosera, and
induces only a moderate amount of inflection. Many acids excite the
glands to secrete an extraordinary quantity of mucus; and the
protoplasm within their cells seems to be often killed, as may be
inferred from the surrounding fluid soon becoming pink. It is strange
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