HOW CERTAIN PLANTS CAPTURE INSECTS. 43 



pitcher one can hardly say for what purpose. The pitcher is tightly closed by a 

 neatly fitting lid when young ; and in strong and healthy plants there is com- 

 monly a little water in it, which could not possibly have been introduced from 

 without. After they are fully grown the lid opens by a hinge ; then a little water 

 might be supposed to rain in. In the humid sultry climates they inhabit it prob- 

 ably does so freely, and the leaves are found partly filled with dead flies, as in 

 our wild Pitcher-plants. 



93. The drowning of insects in plant-pitchers is of course an accidental occur- 

 rence, and any supposed advantage of this to the plant may be altogether fanci- 

 ful. But we cannot deny that the supply of liquid manure may be useful. Be- 

 fore concluding that they are of no account, it may be well to contemplate other 

 sorts of leaf-flytraps. 



94. Sundew as a Fly-catcher. All species of Sundew (Drosera) have their leaves, 

 and some their stalks also, beset with bristles tipped with a gland from which 

 oozes a drop of clear but very glutinous liquid, making the plant appear as if 

 studded with dew-drops. These remain, glistening in the sun, long after dew- 

 drops would have been dissipated. Small flies, gnats, and such-like insects, seem- 

 ingly enticed by the glittering drops, stick fast upon them and perish by starva- 

 tion, one would suppose without any benefit whatever to the plant. But in the 

 broad-leaved wild species of our bogs, such as the common Roimd-leaved Sundew 

 (figured, much reduced in size, at the foot of the vignette title, toward the right), 

 the upper face and edges of the blade of the leaf bear stronger bristles, tipped 

 with a larger glutinous drop, and the whole forms what we must allow to be a 

 veritable fly-trap. 



95. For, when a small fly alights on the upper face, and is held by some of 

 the glutinous drops long enough for the leaf to act, the surrounding bristles 

 slowly bend inwards so as to bring their glutinous tips also against the body of 

 the insect, adding, one by one, to the bonds, and rendering captivity and death cer- 

 tain. This movement of the bristles must be of the same nature as that by 

 which tendrils and some leafstalks bend or coil. It is much too slow to be visible 

 except in the result, which takes a day or two to be completed. Here, then, is a 

 contrivance for catching flies, a most elaborate one, in action slow but sure. And 

 the different species of Sundew offer all gradations between those with merely scat- 

 tered and motionless dewy-tipped bristles, to which flies may chance to stick, and 

 this more complex arrangement, which we cannot avoid regarding as intended for 



