
16 ' FLOWERING PLANTS 
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Kerner suggests that it may expect to find food, or it may be 
seeking shelter from other insects. The fact that only very 
small insects can enter the bladder seems to indicate that they 
are in search of refuge from larger insects. The bladder is 
lined with cells especially adapted for absorbing the products 
of the decaying body; there does not appear to be any special 
digestive juice as in the Pitcher-plant. 
Sundew and Butterwort are abundant in boggy patches of - 
moorland. Both catch animals by movements of their leaves. 
In the Sundew (Plate IL, Fig. 3) the leaves are covered with 
delicate red filaments, largest at the edges; there are about 
200 on a single leaf. Each filament bears at its extremity a 
gland, which secretes a sticky juice that the insect mistakes 
for honey. As an insect alights on the leaf the tentacles bend 
inwards, the tentacle that is first irritated being the one to 
move first ; then movement is set up in the whole fringe of 
tentacles, and the insect cannot escape. The secretion of juice 
by the tentacles is increased as soon as the insect touches 
then:; the juice is acid, and by means of it the nitrogenous 
substances present in the insect’s body are digested. If an 
insect is caught by a marginal tentacle, it is gradually trans- 
ported towards the middle of the leaf, where the digestive 
fluid is poured out in greatest quantity. Digestion takes at 
least a couple of days; the tentacles remain bent during this 
period, and the leat more or less curled up. When digestion. 
is complete, the tentacles straighten themselves, and the leaf 
unfolds. ; 
Butterwort is very abundant on damp moors ; its radical 
leaves form a rosette, and are pressed back against the surface 
of the ground ; being of a yellowish green, they are very con- 
spicuous (Plate II., Fig. 4). The margins of the leaf are 
slightly upturned, forming a kind of trough, and the whole — 
surface 1s covered with glands secreting a sticky fluid. It is 
said that a plant bearing six to nine leaves will have about 
half a million of these glands. An insect alighting on the 
leaf stimulates it, causing the edges to curl over, and the 
sticky fluid prevents the insect’s escape. The presence of the 
