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 proteiaceous 
material, such as bits of meat and white of egg, excite 
movement in the tentacles ; everything else behaves as 
Fic. 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. 
(>) 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 
