GROWTH AND SECRETIONS. 75 



times expelled from the plant by accident or 

 disease, and are almost always capable of removal 

 from one portion of the plant to another. Pro- 

 fessor Henslow gives among the milky juices the 

 following curious instance of a tree called the 

 Cow Tree, from Humboldt : " On the barren 

 flank of a rock grows a tree with dry and leather- 

 like leaves ; its large woody roots can scarcely 

 penetrate into the stony soil. For several months 

 in the year not a single shower moistens its 

 foliage. Its branches appear dead and dried ; 

 yet as soon as the trunk is pierced, there flows 

 from it a sweet and nourishing milk. It is at 

 sunrise that this vegetable fountain is most abun- 

 dant. The natives are then to be seen hastening 

 from all quarters, furnished with large bowls to 

 receive the milk, which grows yellow and thickens 

 at the surface. Some empty their bowls under 

 the tree, while others carry home the juice to 

 their children. The milk, obtained by incisions 

 made in the trunk, is glutinous, tolerably thick, 

 free from all acrimony, and of an agreeable and 

 balmy smell." The milky juices are contained 

 in the bark and leaves, the volatile oils in closed 

 cells, from which they are probably only exhaled 

 in consequence of the permeability of the tissue, 

 whence it happens that the organs which secrete 



