Onapr. X. SENSITIVENESS OF THE LEAVES. 229 
CHAPTER X. 
On tHe SENSITIVFNESS OF THE LEAVES, AND ON THE LINES OF 
TRANSMISSION OF THE Moror ImpuLse. 
Glands and summits of the tentacles alone sensitive — Transmission 
of the motor impulse down the pedicels of the tentacles, and 
across the blade of the leaf— Aggregation of the protoplasm, 
a reflex action — First discharge of the motor impulse sudden — 
Direction of the movements of the tentacles— Motor impulse 
transmitted through the cellular tissue— Mechanism of the move- 
ments — Nature of the motor impulse — Re-expansion of the ten- 
tacles. " 
WE have seen in the previous chapters. that many 
widely different stimulants, mechanical and chemical, 
excite the movement of the tentacles, as well as of the 
blade of the leaf; and we must now consider, firstly, 
what are the points which are irritable or sensitive, 
and secondly how the motor impulse is transmitted 
from one point to another. The glands are almost 
exclusively the seat of irritability, yet this irritability 
must extend for a very short distance below them ; 
for when they were cut off with a sharp pair of 
scissors without being themselves touched, the ten- 
tacles often became inflected. These headless ten- 
tacles frequently re-expanded ; and when afterwards 
drops of the two most powerful known stimulants were 
placed on the cut-off ends, no effect was produced. 
Nevertheless these headless tentacles are capable of 
subsequent inflection if excited by an impulse sent 
from the disc. I succeeded on several occasions in 
crushing glands between fine pincers, but this did 
not excite any movement; nor did raw meat and salts 
of ammonia, when placed on such crushed glands. 
