220 TFIE STORY OF PLANT LIFE 



navel. A similar cavity in the shells of univalve 

 niollusca is also called an umbilicus. 



The name Cotyledon (from the Greek cotule) also 

 alludes to the cup-like form of the leaf. It has been 

 usual recently to add veneris to the second name, 

 meaning Venus's. 



Navel-wort is a typical example of a crevice-plant, 

 or chomophyte, and the suitable habitats for this 

 plant are where rocks are exposed at the surface, 

 and are not covered with soil, or very slightl}'. These 

 hard rocks, since only such types resist the action 

 of weathering for long periods, are chiefly found on 

 the west coast of England and more generally in 

 Scotland. East of the Pennines, with the excep- 

 tion of the newer range of hills in the south, soft 

 and usually calcareous, the country is a vast plain, 

 as in East Anglia (where this plant is absent) and the 

 Midlands. In the plains one cannot expect then to 

 find this plant, but only where the older rocks are to 

 be found on the west coast of England, in Wales, and 

 Scotland, and in Ireland in the west and south-east, 

 generally speaking. It also occurs in the Channel 

 Islands. In Wales it ascends to looo ft., and higher 

 in Yorkshire and Scotland. 



The habitat is a cleft or crevice in rocks, often 

 streaming with water at some seasons, but exposed 

 to drought at others. It is also to be found on 

 walls and buildings, but its natural habitat is rocks, 

 siliceous as a rule. 



The plant has the rosette habit, and is succulent 



