iv.j 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 entomostraca 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 Dioncsa 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 androscemifolium) 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 



