362 ECOLOGY 



Many of them occur in boggy or marshy habitats, usually 

 in soil poor in mineral food ; while some of them are water- 

 plants. In all cases, however, they contain much chloro- 

 phyll in their tissues, and their general mode of nutrition 

 is like that of an ordinary green plant. The animal food 

 obtained by means of their traps is, therefore, only supple- 

 mentary. Still, their capturing devices are ingenious and 

 curious. They may take the form of : (i) sticky hairs or 

 sticky and sensitive tentacles ; (2) trap-like bladders and 

 pitchers; and (3) sensitive leaves which form rapidly- 

 closing traps. 



Two examples, the Sundew (Fig. 232) and Butterwort 

 (Fig. 234, 1,2), are locally abundant in boggy places on 

 the moors, both in hilly districts and on lowland moors. 

 Three species of Sundew occur, the most common one 

 being the Round-leaved Sundew (Drosera rotundifolia) . It 

 is a small plant, only a few inches high, whose slender roots 

 anchor the plant in the wet soil, or among bog moss, and 

 the leaves form a rosette pressed close to the ground. At 

 the end of the leaf-stalk is a circular, reddish blade, fringed 

 with long, clubbed tentacles, and similar, but shorter, 

 tentacles cover the upper surface. The lips secrete a 

 sticky, viscid fluid, forming shining dew-like drops, attrac- 

 tive to insects. The secretion is mistaken for honey, and 

 if a small insect alights on some of the tentacles at the 

 edge of the leaf it is held firmly by the secretion. The 

 tentacles are very sensitive to pressure, and the stimulus 

 given by the insect in its struggles to escape results in the 

 tentacles bending over ; and the stimulus may extend to 

 other tentacles and they also bend over, and so carry the 

 insect to the centre of the blade, where it is brought into 

 contact with other drops and eventually it is smothered 

 (Fig. 233). The secretion of the tentacles is now changed, 

 and a ferment is poured out which digests the protein 

 compounds of the insect's body, and these digested materials 



