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, 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
anomalous; 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. [page 232]
cases; but this is not strictly true, for in three instances a little
syrup was added to the bits of raw meat on the backs of leaves, in
order to keep them damp for a time; and after 36 hrs. there was a trace
of reflexion in the tentacles of one leaf, and certainly in the blade
of another. After twelve additional hours, the glands began to dry, and
all three leaves seemed much injured. Four leaves were then placed
under a bell-glass, with their footstalks in water, with drops of syrup
212