that allied acids act very differently: formic acid induces very slight
inflection, and is not poisonous; whereas acetic acid of the same
strength acts most powerfully and is poisonous. Lactic acid is also
poisonous, but causes inflection only after a considerable lapse of
time. Malic acid acts slightly, whereas citric and tartaric acids
produce no effect. [page 274]
In the ninth chapter the effects of the absorption of various alkaloids
and certain other substances were described. Although some of these are
poisonous, yet as several, which act powerfully on the nervous system
of animals, produce no effect on Drosera, we may infer that the extreme
sensibility of the glands, and their power of transmitting an influence
to other parts of the leaf, causing movement, or modified secretion, or
aggregation, does not depend on the presence of a diffused element,
allied to nerve-tissue. One of the most remarkable facts is that long
immersion in the poison of the cobra-snake does not in the least check,
but rather stimulates, the spontaneous movements of the protoplasm in
the cells of the tentacles. Solutions of various salts and acids behave
very differently in delaying or in quite arresting the subsequent
action of a solution of phosphate of ammonia. Camphor dissolved in
water acts as a stimulant, as do small doses of certain essential oils,
for they cause rapid and strong inflection. Alcohol is not a stimulant.
The vapours of camphor, alcohol, chloroform, sulphuric and nitric
ether, are poisonous in moderately large doses, but in small doses
serve as narcotics or, anaesthetics, greatly delaying the subsequent
action of meat. But some of these vapours also act as stimulants,
exciting rapid, almost spasmodic movements in the tentacles. Carbonic
acid is likewise a narcotic, and retards the aggregation of the
protoplasm when carbonate of ammonia is subsequently given. The first
access of air to plants which have been immersed in this gas sometimes
acts as a stimulant and induces movement. But, as before remarked, a
special pharmacopoeia would be necessary to describe the diversified
effects of various substances on the leaves of Drosera.
In the tenth chapter it was shown that the sensitive- [page 275] ness
of the leaves appears to be wholly confined to the glands and to the
immediately underlying cells. It was further shown that the motor
impulse and other forces or influences, proceeding from the glands when
excited, pass through the cellular tissue, and not along the
fibro-vascular bundles. A gland sends its motor impulse with great
243