INTRODUCTION. 



LIFE is everywhere. " Nature lives" says Lewes ; 

 " every pore is bursting with life ; every death is only 

 a new birth ; every grave a cradle." " The earth-dust 

 of the universe," says Jean Paul, "is inspired by the 

 breath of the great God. The world is brimming with 

 life j every leaf on every tree is a land of spirits." The 

 tendency to vegetate is a ceaseless power. It has been 

 in operation from the earliest ages of the earth, ever 

 since living beings were capable of existing upon its 

 surface ; and so active in the past history of the globe 

 has been this tendency, that most of the superficial 

 rocks of the earth's crust are composed of the remains 

 of plants. It operates with undiminished and tireless 

 energy still. Vegetation takes place upon almost every 

 substance ; upon the bark of trees, upon naked rocks, 

 upon the roofs of houses, upon dead and living animal 

 substances, upon glass when not constantly kept clean, 

 and even on iron which had been subjected to a red heat 

 a short time before. Zoologists tell us, when speaking 

 of animalcules, that not a drop of stagnant water, not a 

 speck of vegetable or animal tissue, not a portion of 

 organic matter but has its own appropriate inhabitants. 

 A 



