530 THE UNIVERSE. 



time made their way to this spot, in order to botanize amid 

 the products of the tropics without fatigue and without peril. 



At other times, in order to satisfy the requirements of 

 commerce or his own pleasure, man extirpates certain spe- 

 cies from their native country in order to enrich distant 

 lands with them. In short, it is sometimes to the armies 

 of conquerors that we owe certain exotic plants 



Yet there are countries which are sometimes invaded by 

 a vegetation neither the arrival nor the vigor of which can 

 be explained. It grows in its new country with such en- 

 ergy that it stifles everything that previously grew in the 

 spots where it fixes itself. Thus a large everlasting, the 

 Ilelichrysum. fetidum, transplanted from America to France, 

 has become a despotic ruler in many of the southern dis- 

 tricts of that country. 



In opposition to this, the common artichoke has exiled 

 itself from France in order to establish itself victoriously in 

 certain districts of Patagonia, and dispossess the rightful 

 owners. In bringing our most useful cereal from Asia we 

 have brought with it the cockle, the wild poppy, and the 

 corn-flower, which enamel our harvests with such lively 

 colors. 



Our wants have caused us to import the greatest part of 

 our alimentary plants from Asia. Wheat evidently comes 

 from Persia ; Michaux and Olivier observed it there in the 

 wild state. The vine, the olive, and the walnut-tree were 

 brought to us from the mountains of Asia. The citron- 

 tree comes originally from Media, and the orange-tree from 

 China. 1 



1 The wild radish (Raphanus raphanislrum, Linn.), often called the white char- 



