CHAP. X. SENSITIVENESS OF THE LEAVES. 22 ( J 



CHAPTER X. 



OM THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OP 



TRANSMISSION OF THE MOTOR IMITI.SE. 



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 He-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. 



