Chap. X. SENSITIVENESS OF THE LEAVES. 231 



that cutting and pricking the leaf does not excite 

 movement. The petiole of the leaf is quite insensible. 



The backs of the leaves bear numerous minute 

 papillae, which do not secrete, but have the power of 

 absorption. These papillae are, I believe, rudiments 

 of formerly existing tentacles together with their 

 glands. Many experiments were made to ascertain 

 whether the backs of the leaves could be irritated in 

 any way, thirty-seven leaves being thus tried. Some 

 were rubbed for a long time with a blunt needle, 

 and drops of milk and other exciting fluids, raw 

 meat, crtished flies, and various substances, placed on 

 others. These substances were apt soon to become 

 dry, showing that no secretion had been excited. 

 Hence I moistened them with saliva, solutions of 

 ammonia, weak hydrochloric acid, and frequently with 

 the secretion from the glands of other leaves. I 

 also kept some leaves, on the backs of which exciting 

 objects had been placed, under a damp bell-glass ; but 

 with all my care I never saw any true movement. I 

 was led to make so many trials because, contrary to 

 my previous experience, Mtschke states* that, after 

 affixing objects to the backs of leaves by the aid of 

 the viscid secretion, he repeatedlij saw the tentacles 

 (and in one instance the blade) become reflexed. 

 This movement, if a true one, would be most ano- 

 malous; for it implies that the tentacles receive a 

 motor impulse from an unnatural source, and have 

 the power of bending in a direction exactly the 

 reverse of that which is habitual to them ; this power 

 not being of the least use to the plant, as insects 

 cannot adhere to the smooth backs of the leaves. 



I have said that no effect was produced in the above 



* * Bot. Zeitung,' 1860, p. 437. 

 11 



