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 rapidity down the pedicel of the same tentacle to the basal part which alone bends.  The impulse, then passing onwards, spreads on all sides to the surrounding tentacles, first affecting those which stand nearest and then those farther off.  But by being thus spread out, and from the cells of the disc not being so much elongated as those of the tentacles, it loses force, and here travels much more slowly than down the pedicels.  Owing also to the direction and form of the cells, it passes with greater ease and celerity in a longitudinal than in a transverse line across the disc.  The impulse proceeding from the glands of the extreme marginal tentacles does not seem to have force enough to affect the adjoining tentacles; and this may be in part due to their length.  The impulse from the glands of the next few inner rows spreads chiefly to the tentacles on each side and towards the centre of the leaf; but that proceeding from the glands of the shorter tentacles on the disc radiates almost equally on all sides.