VEGETATION OF ROCKY PLACES. 6ll 



in but cannot get out. The Venus's fly-trap (Dionaea muscipula, 

 fig. 126) on sandy coastal lowlands of North Carolina is one of 

 the most remarkable of the insectivorous plants. When insects 

 alight on the leaf and irritate the hairs on the surface the leaf 

 closes suddenly and the stout hairs on the edges fit in between 

 one another like the teeth of a steel trap and prevent the escape 

 of the insect, while the surfaces of the leaf are gradually pressed 

 tightly against it, and fluids exuded by the leaf digest the insect. 



1102. A plant atoll. In the morainic regions of central New 

 York there are some interesting and striking examples of the 

 effects of plants on the topography of small and shallow basins. 

 These formations sometimes take the shape of " atolls," though 

 plants, and not corals, are the chief agencies in their gradual evolu- 

 tion. Fig. 484 is from a photograph of one of these plant atolls 

 about fifteen miles from Ithaca, N. Y., along the line of the 

 E. C. & N. R. R., near a former flag-station known as Chicago. 

 The basin here shown is surrounded by three hills, and is formed 

 by the union of their bases, thus forming a pond with no outlet. 



Topography of the atoll-moor. The entire basin was once a 

 large pond, which has become nearly filled by the growth of a 

 vegetation characteristic of such regions. Now only a small, 

 nearly circular, central pond remains, while entirely around 

 the edge of the earlier basin is a ditch, in many places with from 

 30-60 cm of water. There is a broad zone of land then lying 

 between the central pond and the marginal ditch. Just inside 

 of the ring formed by the ditch is an elevated ring extending all 

 around, which is higher than any other part of the atoll. On a 

 oortion of this ring grow certain grasses and carices. The soil 

 for some depth shows a wet peat made up of decaying grasses, 

 carices, and much peat-moss (sphagnum). In some places one 

 element seems to predominate, and in other cases another ele- 

 ment. On some portions of the outer ring are shrubs one to three 

 meters in height, and occasionally small trees have gained a 

 foothold. 



Next inside of this belt is a broad, level zone, with Carex 

 filiformis, other carices, grasses, with a few dicotyledons. Inter- 



