The upper surface of the lobes, as already stated, is thickly covered
with small purplish, almost sessile glands. These have the power both
of secretion and absorption; but unlike those of Drosera, they do not
secrete until excited by the absorption of nitrogenous matter. No other
excitement, as far as I have seen, produces this effect. Objects, such
as bits of wood, cork, moss, paper, stone, or glass, may be left for a
length of time on the surface of a leaf, and it remains quite dry. Nor
does it make any difference if the lobes close over such objects. For
instance, some little balls of blotting paper were placed on a leaf,
and a filament was touched; and when after 24 hrs. the lobes began to
re-open, the balls were removed by the aid of thin pincers, and were
found perfectly dry. On the other hand, if a bit of damp meat or a
crushed fly is placed on the surface of an expanded leaf, the glands
after a time secrete freely. In one such case there was a little
secretion directly beneath the meat in 4 hrs.; and after an additional
3 hrs. there was a considerable quantity both under and close round it.
In another case, after 3 hrs. 40 m., the bit of meat was quite wet. But
none of the glands secreted, excepting those which actually touched the
meat or the secretion containing dissolved animal matter.
If, however, the lobes are made to close over a bit of meat or an
insect, the result is different, for the glands over the whole surface
of the leaf now secrete copiously. [page 296] As in this case the
glands on both sides are pressed against the meat or insect, the
secretion from the first is twice as great as when a bit of meat is
laid on the surface of one lobe; and as the two lobes come into almost
close contact, the secretion, containing dissolved animal matter,
spreads by capillary attraction, causing fresh glands on both sides to
begin secreting in a continually widening circle. The secretion is
almost colourless, slightly mucilaginous, and, judging by the manner in
which it coloured litmus paper, more strongly acid than that of
Drosera. It is so copious that on one occasion, when a leaf was cut
open, on which a small cube of albumen had been placed 45 hrs. before,
drops rolled off the leaf. On another occasion, in which a leaf with an
enclosed bit of roast meat spontaneously opened after eight days, there
was so much secretion in the furrow over the midrib that it trickled
down. A large crushed fly (Tipula) was placed on a leaf from which a
small portion at the base of one lobe had previously been cut away, so
that an opening was left; and through this, the secretion continued to
run down the footstalk during nine days,—that is, for as long a time as
it was observed. By forcing up one of the lobes, I was able to see some
distance between them, and all the glands within sight were secreting
freely.