8 Geographical Distribution of the Cruciferm, 



gathered plentifully on the north shores of the St. Lawrence. 

 The D. hirta, is common on the rocky islands of Lake Supe- 

 rior; and the D. glabella, lutea, and nemorcdis, approach the 

 confines of Canada West. Hooker gives the island of Mon- 

 treal as a habitat of the Draba murcdis of Linnseus. The 

 Draba o£igo&perma r a native of the banks of McKenzie's River, 

 appears to have been collected by Nuttall on the summit of lofty 

 hills near the sources of the Platte. The Rocky Mountains afford 

 near their heights some Drabas peculiar to the range ; the 

 D. densifolia at the sources of Lewis's River, the D. rupestris 

 levipes, crassifolia and aurca, on the same ridges, as far north 

 as lat. 5*7°. The strictly southern species are fewer in num- 

 ber. D. arabisans is found near Lake Champlaiu, and in the 

 States of New York and Michigan, crossing to the north shore of 

 Lake Superior. Five or six others are dispersed only over the- 

 Central and Western States ; but the Z>. verna, with bipartite 

 petals, which may be reckoned among these r sometimes may be 

 seen decking the hill-sides and fields of our province. 



The fifth tribe of Cruciferte, the Alyssinece, commencing with 

 Vesicaria, continued in Draba, will end with Cochlearia, a 

 genus pre-eminently Polar, as encircling to a great extent the 

 Great Polar Basin, representing the great flowering classes almost 

 at the very limits- of vegetation, and bearing* the standard of Flora 

 nearly to the axle of our sphere. Three Cochlear ia belong 

 to Russian America, and four to our Arctic coast. These 

 latter are the C. Anglica r fenestrolis, officinalis, and Danica„ 

 C try dactylites is said, to occur in Labrador, and C, Greenlandica 

 pertains to Greenland. Diffused laterally like a belt or girdle^, 

 this genus, assisted by other plants of a similar constitution, and 

 the Mosses and Lichens, helps to produce an identity of vegetable- 

 growth and covering to the earth in the highest northern latitudes, 

 on the European, Asiatic, and American shores. 



The genus Camelina, from which the sixth tribe of Crucifene,. 

 the Camclinecc, takes name,, has but one species native of North 

 America, the (7. bmharecefolia, which has been found only on* 

 the Russian territory en the north-west coast. The C. sativo 

 must be an introduced plant, and is probably working its way 

 westwards and northwards vvitli the progress of civilization. 



Braya, with the four following genera, has been placed by 

 Torrey, with some degree of doubt, in the tribe Camelimm* 

 The Rrcya alpina is. obtained on the Rocky Mountains, from, 



