in. THE HOSPITALITIES OF NATURE. 53 



ance from the tree, but from the air and soil by means 

 of its genuine roots and green leaves ; and if its stem be 

 severed it will die like any other plant. The ivy is, 

 therefore, a commensal, and not a parasite. Perhaps 

 the most beautiful and striking examples of commensal- 

 ism are the large class of plants called epiphytes, which 

 simply rest upon the trunks and branches of trees, and 

 adorn them with wreaths and garlands such as they 

 themselves could not develop, beautifying the aged 

 structure with new bursts of bud and blossom, and 

 casting even over death a vesture of loveliness which 

 makes the end brighter than the beginning. Orchids 

 are the most familiar representatives of this class. In 

 dense tropical forests they live upon the decaying 

 matter that accumulates on the boughs and in the forks 

 of old trees; or they send out long aerial roots that 

 enter into and feed upon no soil, but extract nourish- 

 ment solely from the moisture and carbonic acid gas of 

 the atmosphere. They have huge gouty joints which 

 contain a store of organized nourishment, from which 

 the materials of the exquisitely-fashioned blossoms are 

 drawn forth ; and the insect-like shapes and colours of 

 these blossoms, and the articulations of their stems, as 

 well as their aerial habitats, point them out as the 

 counterparts in the vegetable kingdom of the insects in 

 the animal. 



In tropical countries this system of mutual accom- 

 modation exists to a large extent. It is created by 

 the exigencies of the situation. The luxuriance of 

 tropical vegetation developed by the hot sun and 



