Ouap. X. SENSITIVENESS OF THE LEAVES. 23] 
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 
papille, which do not secrete, but have the power of 
absorption. These papille 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, crushed 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, Nitschke states* that, after 
affixing objects to the backs of leaves by the aid of 
the viscid secretion, he repeatedly 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. 
16 
