44 COMPOUND ORGANS OF PLANTS. 



The roots of rock plants adhere to their surface and crevices 

 with the most astonishing tenacity ; as for example, the beau- 

 tiful wild columbine, (Aquilegia Canadensis,) one of the early 

 spring flowers of the northern States. 



The roots of plants, particularly, the fibrous and matted 

 roots of the sedge and grass tribe, bind together the loose soil 

 on the sea-shore, and prevent it from drifting inland. On 

 many coasts, the inward drift of the sand by the strong sea 

 breezes which prevail, produces hills of sand called dunes. 

 The safety of these shores is greatly promoted by a species of 

 grass called theArundo arenaria, whose thick and matted roots 

 bind together the loose sand and prevent its desolating effects. 



That disintegration and destruction of rocks mechanically and 

 chemically, which is continually going forward in nature, is 

 also prevented from being carried forward to an injurious 

 extent by the fibrous roots of grasses and other plants. 



It is a fact well known to practical geologists, that when 

 rocks rise above the surface of the earth in cliffs and ridges, 

 they become exposed to the mechanical and chemical action of 

 the atmosphere, and their surface gradually shivers off, crumbles 

 down, and wears away. Hence loose matter collects at the 

 bottom of the escarpment, forming in the course of ages, a 

 slope of disintegrated material, called by geologists a talus. 

 The process of disintegration continues until the talus of fallen 

 fragments has accumulated to the very summit of the escarp- 

 ment, so as to hide it altogether. Now so long as the face of 

 the escarpment is exposed, and the fall of the detached frag- 

 ments continues, vegetation will not seize on the slope ; but 

 when the disintegrated material has acquired that degree of 

 sloping, which is called by geologists, the angle of repose, or 

 has accumulated to the very summit of the escarpment, no 



