*> 





N 



iM 





•\i 



diff . 



• 1 



iv 



ij! 









i'i- 



w.-^ 



<j into i 



^0) 



4' 



r 



OB'*" 







r 



fjf' 



.jC 



f 



Cii. XLIL] 



CHANGES CAUSED BY MAN. 



453 



human art as tlie extensive cultivation of foreign licrbs and 

 shrubs, which, although they are often more nutritious to 

 man, seldoui thrive with the same rank luxuriance as the 



native plants of a district. Man 



IS, m 



truth, continually 



Kow 



striving to diminish the natural diversity of the stations of 

 animals and plants in every country, and to reduce them all 

 to a small number fitted for species of economical use. He 

 may succeed perfectly in attaining his object, even though 

 the vegetation be comparatively meagre, and the total 

 amount of animal life be greatly lessened. 



When St. Helena Avas discovered about the year 150G, 

 it was entirely covered with forests, the trees drooping over 

 the tremendous precipices that overhang the sea. 

 Dr. Hooher, all is changed ; fully five-sixths of the island 

 are entirely barren, and by far the greater part of the vegeta- 

 tion which exists, whether herbs, shrubs, or trees, consists of 

 introduced European, American, African, and Australian 

 plants, which propagated themselves with such rapidity 

 that the native plants could not compete with them. These 

 exotic species, together with the goats, which being carried 

 to the island destroyed the forests by devouring all the 

 young plants, are supposed to have utterly annihilated about 

 100 peculiar and indigenous species, all record of which is 

 lost to science, except those of which specimens were collected 

 by the late Dr. Burchell and are now in the herbarium of Kew."^ 

 In the district of Canterbury, New Zealand, Mr. Locke 

 Travers, writing in 1863, says that the spread of European 

 and other foreign plants is surprisingly rapid. 

 {Polygonum aviculare), the common dock, and the sow thistle 

 grow luxuriantly, the water-cress increases in the still rivers 

 so as to threaten to choke them up altogether, and to put the 

 colonists to the expense of J300 annually in keeping open 



The cow-grass 



stream 



measured 12 feet long 



In some mountain 



and three quarters of an inch in diameter. In some 



districts the white clover is displacing the native grasses, and 



foreign trees, such as poplars, and willows, and the gum- 



* Hooker, Insular Floras, Brit. Assoc. Nottingliani, 1 86G. 



