ORIGIN OF PLANTS. 221 



individuals, of contemporary origin, with which the race be- 

 gan. True, there are some races that have spread over very 

 wide circles, — the circle of the human family has become 

 identical with that of the globe ; and there are certain plants 

 and animals that, from peculiar powers of adaptation to the 

 varieties of soil and climate, — mayhap also from the tena- 

 cious vitality of their seeds, and their facilities of transport 

 by natural means, — are likewise diffused very widely. There 

 are plants, too, such as the common nettle and some of the 

 ordinary gi-asses, which accompany civilized man all over the 

 globe, he scarce knows how, and spring up unbidden wher- 

 ever he fixes his habitation. He, besides, carries with him 

 the common agricultural weeds : there are localities in the 

 United States, says Sir -Charles Lyell, where these exotics 

 outnumber the native plants. But these are exceptions to the 

 prevailing economy of distribution ; and the circles of species 

 generally are comparatively limited and well defined. The 

 mountains of the southern hemisphere have, like those of 

 Switzerland and the Scotch Highlands, their forests of coni- 

 ferous trees ; but they furnish no Swiss pines or Scotch firs ; 

 nor do the coasts of New Zealand or Van Dieman s Land 

 supply the European shells or fish. True, there is much to 

 puzzle in the identity of what may be termed the exceptional 

 plants, equally indigenous, apparently, in circles widely se- 

 parated by space. It has been estimated that there exist 

 about a hundred thousand vegetable species ; and of these, 

 thirty antarctic forms have been recognised by Dr Hooker 

 as identical with European ones. Had Robinson Crusoe failed 

 to remember that he had shaken the old corn-bag where he 

 found the wheat and barley ears springing up on his island, 

 he might have held that he had discovered a new centre of 

 the European ceralia. And the process analogous to the 

 shaking of the bag is frequently a process not to be remem- 

 bered. There are several minute lochans in the Hebrides 



