366 ECOLOGY 



exists, some leaves having normal flat green blades, and 

 others being transformed into pitchers. 



A more complicated device is found in the Venus' 

 Fly-trap {Dionaea muscipula) (Fig. 234, 7 and 8), a plant 

 growing in mossy places in the woods of Carolina. Its 

 leaves, like those of the Butterwort, form a rosette close to 

 the ground ; the leaf -stalk is winged (phyllode), and the 

 blade, slightly bent upwards along the midrib, is fringed 

 with long, comb-like teeth. Many glandular hairs cover the 

 upper surface, and on either side of the midrib are three 

 long jointed hairs (Fig. 234, 7 h). These are sensitive, but 

 if slightly touched once no result is observable ; if, however, 

 a second stimulus is soon applied the blade suddenly closes, 

 and if an insect supplies the stimulus it is at once entrapped. 

 The teeth along the edges interlock, and the two halves of 

 the blade draw close together. A digestive secretion is 

 now poured out over the body of the insect and the digested 

 materials are absorbed by the leaf. Later it expands in 

 readiness for more food. 



The advantage to insectivorous plants of this mode of 

 nutrition is in the gain of nitrogen and nutritive salts sup- 

 plied with the nitrogen compounds, and the plants thus 

 supplied with animal food thrive better than those living 

 solely on inorganic materials. 



CHAPTER XXX 



GRASS-LANDS : PASTURES AND MEADOWS 



A large part of the British Islands is devoted to pastur- 

 age, about one-half of England, three-quarters of Wales, 

 one-half of Scotland, and three-quarters of Ireland being 

 so utilized. Some of this is mountain and heath land, but 

 the greater part is permanent pasture dominated by grasses. 



