158 THE BOG. 



flourish in arid situations, where one would sup- 

 pose that no vegetable could long exist. For a 

 short time only they are exposed to rain, and then 

 they put forth their splendid flowers. During 

 the remainder of the year their roots serve only 

 to fix them to the soil, which is too dry to afford 

 them any nourishment ; but, notwithstanding this, 

 they are then quite as juicy and as vigorous as if 

 they grew in the most highly favoured soil. 



The celebrated traveller Humboldt gives the 

 following description of a tree, the Palo de vaca, 

 or Cow-tree, of South America, an account of 

 which will serve well to illustrate my subject. He 

 says : " On the barren flank of a rock grows a 

 tree, with coriaceous* and seemingly dry leaves. 

 Its large woody roots can scarcely penetrate into 

 the stone. For several months in the year, not a 

 shower moistens its foliage. Its branches appear 

 dead and dried ; but, when the trunk is pierced, 

 there flows from it a sweet and nourishing milk. 

 It is at the rising of the sun that this vegetable 

 fountain is most abundant. The blacks and na- 

 tives are then seen hastening from all quarters, 

 furnished with large bowls to receive the milk, 

 which grows yellow, and thickens at its surface. 

 Some employ their bowls under the tree itself, 

 others carry the juice home to their children. "We 

 seem to see the family of a shepherd, who distri- 

 butes the milk of his flock." A tribe of plants 

 common in our country, the Stone-crops, is scarcely 

 less remarkable. They have very succulent stems 

 and leaves, though growing in situations where for 

 long periods they must be deprived of any nutri- 



* Like leather. 



