Geographical Distribution of the Cruciferce. 9 



latitude 52° to 57° ; and the B. glabella and pilosa are the 

 d's^overies of Sir John Richardson, on the shores of the Arctic 

 Sea, the latter having been met with only at the outlet of McKen- 

 zie River. 



Platypetalum puvpurascens has a habitat extending from 

 McKenzie River to Spitzbergen, and the P. dubium is a species of 

 Melville Island. 



Two Eutremw, the E.Edwardsii, upon which R. Brown founded 

 the genus, and the E. arenicola, are both Arctic plants. The 

 former was discovered first on Pa*ry's voyage to Melville Island, 

 and was afterwards collected, along with the second, on the Arctic 

 coast, on each side of the McKenzie, by the travellers Franklin 

 and Richardson. 



A single species of the genus Platyspermum, the P.scapigerum 

 was the discovery of David Douglas, at the great Falls of the 

 Oregon or Columbia River. 



The Subularia aquatica of Linnaeus has been procured from 

 the borders of ponds in Maine by Nuttall. 



Two tribes having the silicle compressed, contrary to the nar- 

 row septum, will now complete what has to be said regarding the 

 Siluculos^e and their distribution. These are the Thlaspidinece 

 and Lepedinece. 



The Thlaspi arvense of Linnasus, as well as the Thlaspi at- 

 pestre, are commonly met with in old waste grounds in Canada. 

 Both I believe to have been introduced, for neither of them occur 

 to my knowledge in the newly-settled or the uncultivated and 

 wilder parts of the country. Tbe Thlaspi alliaceum is rare. 

 The indigenous species T. montanum is found from Canada to the 

 Arctic zone ; and the T. cochleariforma, closely resembling it, 

 occupies a western position, about the head waters of the 

 Oregon. The T. tuberosum, remarkable for its tuberiferous 

 roots, does not appear to have been met with in Canada or the 

 North. It was discovered by Nuttall in Western Pennsylvania. 



Hutdiinsia, another genus of this tribe Tldaspidinice, has a 

 species, the H. calycina,* from the Rocky Mountains, in lat. 52° 

 to 57° ; a variety of it is noted as native in Kotzebue's Sound. 



The Lepldium ruderale occurs frequently throughout the Bri- 

 tish Possessions from Hudson's Bay to the Pacific Ocean, prefer- 

 ring waste places like the Thlaspi. The L. campestre, common 

 about fields and gardens, is a weed introduced from England. 

 Species are met with passing the Rocky Mountains into the 



