GEOGRAPHY OF PLANTS. 55 



Europe, that some modern botanists have questioned its exotic origin. It 

 is equally common, in the neighbourhood of cultivation, in South Africa, and 

 is spreading in Australia. 



The recent appearance of Anacharis alsinastrum in English canals 

 and rivers is a remarkable instance of the rapid dissemination of mis- 

 chievous exotics. These and several other plants — some of them trouble- 

 some weeds — Europe owes to America ; but she has more than returned 

 the gift in the number of species she has transmitted, and the extent of 

 surface they cover. Whoever has travelled through the United States 

 must have been struck with familiar road- side, hedge, and field- weeds, 

 reminding him of home. Two species of mullein (Verbascum Thapsus and 

 V. Uattaria) are specially common by roadsides, and in recent clearings 

 and along the borders of railway cuttings, as if their seeds were widely and 

 abundantly dispersed in the soil ; yet they are unquestionably introduced 

 from Europe. The Leucanthemum vulgare (ox-eyed daisy) is a far more 

 troublesome weed in America, its adopted home, than it is in Europe ; and 

 so of many other European weeds, now rapidly extending with cultivation 

 over the whole surface of North America. In Australia there is no native 

 species of thistle ; but European thistles have become such pests, even in 

 the recently settled colony of Victoria, that the legislature has been obliged 

 to pass an Act, enforcing penalties on the farmer who shall not duly eradi- 

 cate the thistles on his ground. In Tasmania, the sweet briar (Rosa ru- 

 biginosa), though but a few years ago introduced to gardens as a memento 

 of home, has become wild, and in some districts already forms dense thickets 

 which extend rapidly year by year, the innumerable hips being dispersed 

 by birds. In many places already it must be regarded as a pernicious 

 weed. Vlex europceus (the furze-bush) has likewise escaped in Tasmania, 

 and, as on the highlands of St. Helena, flourishes abundantly. Anthem is 

 nobilis is also completely naturalized, and in some places we have seen 

 whole fields occupied with it, almost to the exclusion of other herbage. 



To the chapter on naturalizations succeeds a history of cultivated plants, 

 tracing the origin of the species most notably cultivated for their roots, 

 tubers, bulbs, stems, leaves, flowers, fruits, or seeds. At the head of the list 

 stands the Potato (Solanum tuberosum), which is stated to have been 

 found in cultivation, at the time of the discovery of America, " in all tem- 

 perate regions from Chili to New Grenada, but not in Mexico." (Humb.) 

 The fact of its having been also cultivated by the aborigines of North 

 Carolina, from which place its roots were brought by Raleigh, is questioned, 

 and we think justly so, the authorities in support of the story being few 



