6 Geographical Distribution of the Craciferce. 



United States, but the S. Sophia, which appears in various 

 localities in Lower Canada, may be a native; a point, however, 

 not easy to be determined. Common to British America and the 

 United States is the very generally diffused Sisymbrium canes- 

 cens, which is also found on the Rocky Mountains, and westward 

 to Oregon and California. This soft-looking, frequently hoary 

 plant, is very hardy, bearing the rigours of the north as well 

 as the heats of Georgia and Arkansas. The S. Sophioides of 

 Fischer, found in high latitudes, extends from Hudson's Bay to 

 the Arctic coast, stretching westward round the continent to the 

 Pacific. It is remarkable amongst its kind by the flowers and 

 pods being in umbelliform corymbs. The S. junceum is from 

 dry stony grounds in the Oregon. Six or seven other species, 

 the discoveries of Nuttall, are found on the hills of the great 

 dividing ridge, south of 49 ; but it is very probable that some if 

 not all of these will be met with by Monsieur Bourgeau, the 

 French botanist attached to Palliser's exploring party, which has 

 been busy last season on the Bow River, and near the boundary 

 line, where it crosses the back-bone of America. In that quarter, 

 hitherto so dangerous, and therefore seldom or never approached 

 by the foot of civilized man, there is a portion of both prairie and 

 mountain yet unsearched, its geology and its botany only dedu- 

 cible from what is known of districts far removed from it. We 

 may therefore anticipate a most interesting description of novelties, 

 in the natural history of the region in question, when the survey- 

 ing and exploring expeditions bring the fruits of their labors 

 before the public. In concluding my remarks on the present 

 genus, I may observe that the S. humile, a Siberian species, is 

 also a production of the Rocky Mountains, but in the higher lati- 

 tudes, from 52° to 68°. The Sisymbrium Thalianum, the Arabis 

 Thaliana of Linnaeus, has been introduced from Europe. 



Passing the Tropidocarpa of Hooker, natives of California, we 

 come upon the genus Erysimum, which contains some hand- 

 some species, shewing themselves on the plains, and on the 

 dry grassy spots throughout the north. The E. cheiranthoides, 

 known in Europe, is also gathered in Canada and the United 

 States, and in the prairie country. We find it west of the Rocky 

 Mountains in hit. 47°, as far as the Pacific ; and Hooker gives it 

 a place on the banks of the McKenzie, up to 67°. The E* 

 lanceolatum, a handsome little plant, appears in the flora of 

 Canada, and, proceeding northwards, reaches the Arctic Sea- 



