The secretion from the taller glands differs in a remarkable manner
from that of Drosera, in being acid before the glands have been in any
way excited; and judging from the changed colour of litmus paper, more
strongly acid than that of Drosera. This fact was observed repeatedly;
on one occasion I chose a young leaf, which was not secreting freely,
and had never caught an insect, yet the secretion on all the glands
coloured litmus paper of a bright red. From the quickness with which
the glands are able to obtain animal matter from such substances as
well-washed fibrin and cartilage, I suspect that a small quantity of
the proper ferment must be present in the secretion before the glands
are excited, so that a little animal matter is quickly dissolved.
Owing to the nature of the secretion or to the shape of the glands, the
drops are removed from them with singular facility. It is even somewhat
difficult, by the aid of a finely pointed polished needle, slightly
damped with water, to place a minute particle of any kind on one of the
drops; for on withdrawing the [page 335] needle, the drop is generally
withdrawn; whereas with Drosera there is no such difficulty, though the
drops are occasionally withdrawn. From this peculiarity, when a small
insect alights on a leaf of Drosophyllum, the drops adhere to its
wings, feet, or body, and are drawn from the gland; the insect then
crawls onward and other drops adhere to it; so that at last, bathed by
the viscid secretion, it sinks down and dies, resting on the small
sessile glands with which the surface of the leaf is thickly covered.
In the case of Drosera, an insect sticking to one or more of the
exterior glands is carried by their movement to the centre of the leaf;
with Drosophyllum, this is effected by the crawling of the insect, as
from its wings being clogged by the secretion it cannot fly away.
There is another difference in function between the glands of these two
plants: we know that the glands of Drosera secrete more copiously when
properly excited. But when minute particles of carbonate of ammonia,
drops of a solution of this salt or of the nitrate of ammonia, saliva,
small insects, bits of raw or roast meat, albumen, fibrin or cartilage,
as well as inorganic particles, were placed on the glands of
Drosophyllum, the amount of secretion never appeared to be in the least
increased. As insects do not commonly adhere to the taller glands, but
withdraw the secretion, we can see that there would be little use in
their having acquired the habit of secreting copiously when stimulated;
whereas with Drosera this is of use, and the habit has been acquired.
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