= - wy 
Iv.] PREDATORY PLANTS. 65 
very finely divided. The delicate yellow flowers rise 
out of the water, but the most curious feature of it 
is the possession of a number of small bladders on 
its roots, stems, and leaves, These doubtless serve 
the same purpose as the air bladders of fucus and 
other sea-weeds, floating the plant to the surface 
when distended with air; but they have also another 
function. There is an opening to each, and this 
opening is closed by a valve which opens inwards 
only. Through this opening numbers of small aquatic 
insects and extomostraca enter. What induces them 
to do so is not known; but they enter, and there is 
no escape. There is no acid secretion from the walls 
of their prison-house, as in Drosera and Dion@a—no 
digestion takes place, but the prisoner remains until 
death and decomposition ensue, when it is absorbed 
by the walls of the bladder. 
The North American Fly-trap or Dog’s Bane 
(Apocynum androsemifolium) is now tolerably well 
known as an enemy to insects. In the corolla tube 
there are five scales which secrete honey, and which 
are irritable. Insects are attracted to the honey, but 
on touching—and consequently exciting—the scales, 
they all bend towards the centre of the flower. In 
consequence of this movement the insects are held 
prisoners in the corolla, where they remain for life— 
which is not a long period. In this and in several 
other species we shall have to notice, neither diges- 
tion nor absorption takes place, and it would there- 
fore seem to be no advantage to the plant to have 
these insectivorous habits; but the insects really 
serve a purpose in the fertilisation of the plant, as 
E 
