WEEDS 203 



in Europe. Let us cite a few examples in proof. 

 In Australia, such European weeds as the Bathurst 

 Burr (Xanthium spinosum), the Noogoora Burr 

 (Xanthium strumarium\ the Spear-thistle, the Sweet- 

 briar and the Stinging Nettle have spread far and 

 wide, and often constitute a real plague. In New 

 Zealand our Dock, Water-cress and Sow-thistle 

 have multiplied so as to require proscription by law. 

 In St. Helena the native vegetation has almost 

 disappeared before man and the plants and animals 

 which he has brought with him. Our common annual 

 grass (Poa annud] thrives in many parts of South 

 America, and our Shepherd's-purse, as well as our 

 common corn-weeds, have become dispersed over 

 almost the whole world. The most troublesome 

 weeds of the United States are said by Asa Gray to 

 be of British origin. It is the same with the animals. 

 Our Rabbit and Rat and Pig and House-fly and 

 Drone-fly seldom find a country in which they cannot 

 multiply. The Horses of the Spanish conquerors ran 

 wild and increased prodigiously in America. 



But there is no reciprocity in the matter. Southern 

 plants, and more rarely southern animals, do now and 

 then get access to Europe, but they cannot maintain 

 themselves here. All kinds of foreign plants are 

 brought over in ballast or wool, and for a season or 

 two they come up where they may chance to be 

 thrown out, but when the supply ceases, native plants 

 quickly take their place. Many an attempt has been 

 made to establish the flowers of the Cape or South 

 America in places of similar climate in Europe, but 

 they have been uniform failures. The Agave (in- 



