ON THE MODES OF DISTRIBUTION OF PLANTS. 375 



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 one hundred 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 at Kew." 



Dr. Burchell himself sowed on a point of this island, in 1845, seeds 

 of Chenopodium ambrosioides, and it multiplied so rapidly that, in four 

 years, it became one of the commonest weeds on the island, and has 

 maintained its ground ever since.* Erigeron Canadense, introduced 

 from America into Europe, has become there one of the commonest 

 weeds, and is now naturalized all over the country, f Datura stramo- 

 nium, now known over almost all Europe and North America, was in- 

 troduced from the East Indies by the gypsies, who used the seeds as a 

 medicine. J (Enothera biennis, introduced from America into Europe 

 by the French, on account of its esculent roots, in 1674, has since 

 spread so that it now grows wild in almost every country in Europe, 

 in the hedges and about the villages. Our agave and Opuntia vul- 

 garis have both been so extensively naturalized in the south of Europe, 

 and they form so conspicuous a feature in the landscape that they have 

 been noticed by many travelers and recorded as indigenous. || Ana- 

 charis Canadensis (water-weed) was introduced into England in 1841, 

 and spread so rapidly that it has become a nuisance by impeding navi- 

 gation in rivers and canals, in spite of efforts made to eradicate it. ^[ 

 Strange to say, nothing of the kind is complained of here in its native 

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

 Travers, writing in 1863, says Polygonum aviculare (common dock) 

 and sow-thistle (Sonchics) grow luxuriantly ; the water-cress increases 

 in the still waters and rivers so rapidly as to threaten to choke them 

 up entirely, and to put the inhabitants to the expense of 300 annually 

 to keep open a single stream. Stems of this cress have been measured 

 twelve feet long and three fourths of an inch in diameter. " In some 

 mountain districts the white clover is displacing the native grasses; and 

 foreign trees, such as poplars and willows, and gum-trees of Australia, 

 are growing rapidly." ** 



All these plants have been introduced into the different countries 

 by man's agency. Numbers of seeds are no doubt conveyed in the 

 raw-hides taken from one country to another. De Candolle says he 

 found numbers of exotic plants growing in the vicinity of a place in 

 the south of France where the hides brought by ships were washed 

 and cleaned. Ballast-heaps near large seaport towns are favorite 

 places of resort for resident botanists, who there often reap rich har- 



* Lyell, "Principles of Geology," ii., p. 402. f Jussieu, "Elementary Botany," p. 717. 

 X Willd., " Botany," p. 419. Willd., ibid., p. 420. 



|| Jussieu, ibid., p. 717. Tf Lyell, he. tit., ii., pp. 401, 402. 



* * Lyell, he. eit., ii., p. 458. 



