12 DROSERA ROTUNDIFOLIA. [Cuap. I. 
the other hand, tartrate of antimony produces no such effect. 
Immersion in many acids (of the strength of one part to 437 
of water) likewise causes a wonderful amount of secretion, SO 
that, when the leaves are lifted out, long ropes of extremely 
viscid fluid hang from them. Some acids, on the other hand, 
do not act in this manner. Increased secretion is not 
necessarily dependent on the inflection of the tentacle, for 
particles of sugar and of sulphate of zinc cause no movement. 
It is a much more remarkable fact, that when an object, 
such as a bit of meat or an insect, is placed on the disc of a 
leaf, as soon as the surrounding tentacles become considerably 
inflected, their glands pour forth an increased amount of 
secretion. I ascertained this by selecting leaves with equal- 
sized drops on the two sides, and by placing bits of meat on 
one side of the disc ; and as soon as the tentacles on this side 
became much inflected, but before the glands touched the 
meat, the drops of secretion became larger. This was 
repeatedly observed, but a record was kept of only thirteen. 
cases, in nine of which increased secretion was plainly 
observed; the four failures being due either to the leaves 
being rather torpid, or to the bits of meat being too small to 
cause much inflection. We must therefore conclude that the 
central glands, when strongly excited, transmit some in- 
fluence to the glands of the circumferential tentacles, causing 
them to secrete more copiously. 
It is a still more important fact (as we shall see more fully 
when we treat of the digestive power of the secretion), that 
when the tentacles become inflected, owing to the central 
glands having been stimulated mechanically, or by contact 
with animal matter, the secretion not only increases in 
quantity, but changes its nature and becomes acid; and this 
occurs before the glands have touched the object on the 
centre of the leaf. This acid is of a different nature from 
that contained in the tissue of the leaves. As long as the 
tentacles remain closely inflected, the glands continue to 
secrete, and the secretion is acid; so that, if neutralised by 
carbonate of soda, it again becomes acid after a few hours. I 
have observed the same leaf with the tentacles closely in- 
flected over rather indigestible substances, such as chemi- 
cally prepared casein,* pouring forth acid secretion for eight 
* [These observations are not trustworthy, owing to the mode of preparation 
of the casein. See p. 95.—F. D.] 
