1861.] REVIEW. 347 



Besides these there are 23 introduced British plants, or they 

 assumed to be such, viz. Ranunculus acris, Capsella Bursa-pas- 

 toris, Silene noctiflora, Agrostemma Githago, Oxalis stricta, Tri- 

 folium pi-atense, T. repens, Achillea Millefolium, Leucanthemum 

 vulgare, Tanacetuni vulgare, Cirsium lanceolatum, C. arvense, 

 Taraxacum Dens-leonis, Plantago major, Verbascum Thapsus, 

 Galeopsis Tetrahit, Cynoglossum officinale, Chenopodium album, 

 Polygonum Persicaria, Rumex Acetosella, Phleum pratense. 



Thus there are, it appears, 60 of the 276 phsenogamous species 

 in the Ottawa district, common to both hemispheres, either by 

 nativity or introduction, or rather more than one-fifth, and fewer 

 than one-fourth, are found growing spontaneously in both con- 

 tinents. 



This is a large proportion of plants common to the two conti- 

 nents of Europe and America, and especially when it is considered 

 that there is a wide ocean between them. 



The number of Ferns and Fern allies recorded as found in this 

 district is 33, and nearly the half of them, or 15, are common 

 both to the British Isles and to America. Of the lower families 

 nearly all the registered species are common to both continents. 



It would be an interesting question for botanical geographers 

 to solve, viz. whether or not there be as many British plants in 

 an equal area of Independent Tartary as there are in the small 

 section of Upper Canada of which a botanical list is given in the 

 'Canadian Naturalist^ now before us. The question is — Are 

 there as many British plants as one-fourth or one-fifth of the 

 entire vegetation in the district round the Sea of Aral, and in 

 the countries known by the names of Turkistan and Bucharia? 

 This tract is about as far east as the basin of the Ottawa is west 

 of London. In solving the question about the migration of 

 plants westward, as the great wave of population has flowed from 

 the east to the west, it should be taken into consideration that 

 land is almost continuous from Asia through Europe from east 

 to west, or vice versd, while between Europe and America the 

 continuity is interrupted by the Atlantic Ocean. 



This would probably be productive of more interesting and 

 more practical results than the futile attempts to assign geogra- 

 phical limits to objects which are as liable to change in their re- 

 lations as the earth's surface, which is altered by the increase of 

 population, migrations of people, and the like. The idle disputes 



