232 $ 0&EST LANDS OF NORTtlEKN RUSSIA. 



The maximum of the genus Erica is at the Cape of Good 

 Hope ; but members of the Heath family extend to northern 

 regions in the form of Erica Tetralix, E. cinerea, and Cal- 

 luna vulgaris. The tropical Myrtaceae have Myrtus com- 

 munis to represent them in Europe, Leptospermese in 

 Australia, and Metrosideros lucida in Lord Auckland's 

 Group, lat, 50J S. 



' An order, or a genus, or a species, in one country is 

 occasionally represented in another by forms which are 

 either allied, or have physiognomic resemblance. There is 

 thus sometimes a repetition of resembling or almost similar 

 forms in countries separated by seas or extensive tracts of 

 land. The Ericacese of the Cape have in Australia a 

 representative in the nearly allied Epacridacese ; the 

 Cactaceae of America are represented by certain succulent 

 forms of Mesembryanthemaceae andEuphorbiaceae in Africa; 

 and by some Crassulaceae in Europe. Trientalis europsea 

 has a representative form in America, T. americana ; 

 Cornus suecica occurs in Europe, C. canadensis in Canada. 

 Empetrum nigrum, in Arctic regions, has E. rubrum to 

 take its place in the antarctic ; Pinguicula lusitanica, in 

 the northern hemisphere, has P. antarctica closely resem- 

 bling it in the southern ; Hydnora africana and H. triceps 

 in South Africa are represented in South America by H. 

 americana. 



' The mode in which the globe has been clothed with 

 vegetation has given rise to much discussion. We know 

 from the Sacred Record, that on the third day of the 

 Creation the earth brought forth grass, and herb yielding 

 seed after his kind, and the tree yielding fruit after his 

 kind ; but whether the whole earth was at once clothed 

 with vegetation, or certain great centres were formed, 

 whence plants were gradually to spread, we have no means 

 of knowing. The endemic limitation of certain orders, 

 genera, and species, would certainly lead to the opinion, 

 that, in many instances, there have been definite centres, 

 whence the plants have spread only to a certain extent. 

 But the general distribution of other tribes of plants, and 



