130 



BRITISH PLANTS 



the centre, while other glands, sessile upon the surface, 

 pour over the unfortunate victim a digestive fluid. This 

 secretion is similar in nature and effect to the digestive 

 juices present in the stomach of animals. The insect is 

 quickly killed, and the nitrogenous constituents of its 

 body are dissolved and absorbed into the leaf. It is 

 curious that only small fragments of proteinaceous 

 material, such as bits of meat and white of egg, excite 

 movement in the tentacles ; everything else behaves as 



FIG. 44. Drosera longifolia (SUNDEW). 



dust, to which the tentacles are absolutely insensible. 

 Darwin, however, found that the tentacles are sensitive 

 to traces of ammonium- salts. 



(b) Pinguicula vulgaris (Fig. 45), the butterwort, is 

 common in peat-bogs, especially in mountainous districts. 

 In North Wales it is remarkably abundant above 

 1,000 feet. This is another rosette-plant with a few 

 ovate fleshy leaves, covered with sessile glands, some 

 of which secrete a digestive liquid, and others sticky 

 mucilaginous drops. The leaves always remain open, 

 and in dry, sunny weather, when the air is filled 



