VEGETABLE PARASITES. 149 



merely to draw attention to the fact of its existence. 

 The observant man however cannot go far through a 

 great forest without being struck with the vast swarms 

 of insect life which it contains; every living tree is a 

 museum of entomological research there is scarcely a 

 leaf, or a portion of bark, that does not contain its 

 own special form of parasite which feeds upon its 

 juices or its substance and does it begin to decay? or 

 does it fall and die ? Why then, each of those periods 

 of change breeds its multitudes, which feed upon de- 

 caying or dead wood. Even the solid heart of the 

 timber itself becomes honey-combed by various kinds 

 of borers, which finally reduce it to impalpable touch- 

 wood, till at last the final stage of disintegration is 

 reached which we have already noticed a few pages 

 back. 



Then as regards the vegetable forms of parasitic 

 life How protean is their abundance, their variety, 

 and their ubiquity ! Countless varieties of lichens and 

 mosses cover the limbs and trunks of every living tree, 

 the surface of every rock or bank of earth. The 

 smoothest and hardest stone for instance that can be 

 placed there, does not long remain exempt from some 

 form of parasitic growth. Shortly some little yellowish 

 or greenish discoloration becomes apparent on portions 

 of its surface, marking the impress of the wearing finger 

 of time ; and showing by its existence that even there 

 the process of decomposition and disintegration has 

 already begun, to whose unceasing operation we have 

 already referred. 



Then again every stage of decay is marked by its 

 own special form of growth first the lichen, then the 

 fungus, the moss, the fern, and finally the new genera- 



