PHYSIOGNOMY OF PLANTS. 215 



low and oleaginous marine plants. The history of the vege- 

 table covering and of its gradual extension over the barren 

 surface of the earth, has its epochs, as well as that of the 

 migratory animal world. 



But although life is everywhere diffused, and although the 

 organic forces are incessantly at work in combining into new 

 forms those elements which have been liberated by death; 

 yet this fulness of life and its renovation differ according 

 to difference of climate. Nature undergoes a periodic stag- 

 nation in the frigid zones; for fluidity is essential to life. 

 Animals and plants, excepting indeed mosses and other 

 Cryptogamia, here remain many months buried in a winter 

 sleep. Over a great portion of the earth, therefore, only 

 those organic forms are capable of full development, which 

 have the property of resisting any considerable abstraction 

 of heat, or those which, destitute of leaf-organs, can sustain 

 a protracted interruption of their vital functions. Thus, the 

 nearer we approach the tropics, the greater the increase in 

 variety of structure, grace of form, and mixture of colours, 

 as also in perpetual youth and vigour of organic life. 



This increase may readily be doubted by those who have 

 never quitted our own hemisphere, or who have neglected the 

 study of physical geography. When in passing from our 

 thickly foliated forests of oak, we cross the Alps or the 

 Pyrenees and enter Italy or Spain, or when the traveller first 

 directs his eye to some of the African coasts of the Mediter- 

 ranean, he may easily be led to adopt the erroneous inference 

 that absence of trees is a characteristic of hot climates. But 

 they forget that Southern Europe wore a different aspect, 

 when it was first colonised by Pelasgian or Carthaginian 

 settlers ; they forget too that an earlier civilization of the 

 human race sets bounds to the increase of forests, and that 

 nations, in their change -loving spirit, gradually destroy the 

 decorations which rejoice our eye in the North, and which, 

 more than the records of history, attest the youthfulness of 



