Cuav. XL] GENERAL SUMMARY. 221 
mitting 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 move- 
ment 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 subséquent 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 anesthetics, 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 sensitiveness 
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 
