III. INTRODUCED SPECIES. 123 



affect those arithmetical comparisons to which phyto- 

 geographers commonlj^ seem to attach much importance. 

 It appears that the flora of Britain must now include up- 

 wards of three hundred species (320 to 330, by the lists 

 before printed) which are known, believed, or conjectured 

 to have been introduced into this island by the agency of 

 mankind, either intentionally or accidentally. The, 

 foreign ingredient thus constitutes nearly one-fifth of the 

 flora, reckoned b}^ species, after striking out of the long 

 list several of the least suspected and of the least esta- 

 blished species. This admixture of disputed natives is 

 distributed very unequally among the groups of technical 

 botany. The Gramina and Liliacece are largely increased 

 in their numbers thereby ; while, of their two not distant 

 allies, CyperacecB are scarcely changed, and Orchidaceee 

 quite unchanged, in numbers. The small orders Fuma- 

 riacece, Papaveracecs, Vcderianacece, and Amaryllidacece 

 are very largely increased, in proportion to their actual 

 number of included species. And some very small 

 orders are represented by the disputed natives only, as 

 Tamariscacece, Balsaminacece, Apoeynacete, &c. 



Statistical summaries, both absolute and comparative, 

 might thus be much varied according to the exclusion or 

 inclusion of so large a number and proportion of dispu- 

 tably indigenous species. In comparing together the 

 floras of Britain and New Zealand, for example, there 

 would at present be much more of the artificial admixture 

 to be allowed for in that of the former country. In com- 

 paring together sections or provinces of the same country, 

 as England with Scotland, or Thames with Severn, the 

 effect of their introduced species might be nearly equalised 

 in the general result. But in other comparisons, for ex- 

 ample, between the floras of the Agrarian and Arctic 

 regions, the results would be considerably affected ; since 



