
‘ECOLOGICAL CLASSIFICATION OF PLANTS: © 15 
_ of special apparatus generally developed in connection with the 
leaf. These plants may be divided into two groups according 
to the nature of the apparatus. | 
1. Those that catch insects by means of traps—e. Jy Pitcher 
plant, Bladderwort. | 
2. Those that perform. movements in the capture of their 
prey—Sundew, Butterwort. In each case the means of 
attracting the insect, its capture, and the arrangements for 
digestion, must be considered. 
In the Pitcher-plant (Nepenthes), which belongs to éropical 
regions, but may be seen in English greenhouses, the petiole 
is modified into three parts—a leaflike branch or phyllode, a 
tendril, and a pitcher (Plate I.). The lamina of the leaf — 
forms the lid of the pitcher, the whole apparatus being a 
regular trap, into which the insect is enticed. It is attracted 
_ by the brightly coloured streaks on the lid and by the honey 
on the under side of the lid and round the mouth of the 
pitcher. It is captured by bristles round the rim of the 
pitcher ; these bristles point inwards, so that the insect can- 
not escape backwards, and as the inside of the pitcher is 
slippery, it loses its foothold, falls into the liquid at the 
bottom, and is quickly drowned. As soon as the insect 
reaches the bottom of the pitcher, more liquid is secreted ; 
this contains an acid, by which the body of the insect 1s 
digested ; the cells lining the pitcher absorb the products otf 
digestion. The function of the tendril is to enable the Pitcher- 
plant to grasp other plants, which may be more conveniently 
situated for the capture of insects. 
Bladderwort (U¢ricularia) is abundant in little pools of still 
water in peat-bogs. Here the trap takes the form of a bladder 
developed instead of leaves on some of the threadlike stems. 
Hach bladder has a valve which opens inwards (Plate IT., Fig. 2). 
An insect pressing against it pushes it in, but as soon as the 
insect has entered the bladder and is no longer pressing © 
against the valve, the elasticity of the valve makes it spring 
back and close the opening. The insect then cannot escape. 
What attracts the insect to the bladder is not known; 
ae 
