232 FOREST LANDS OF NORTHERN 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 Myrtacee have Myrtus com- 
munis to represent them in Europe, Leptospermez in 
Australia, and Metrosideros lucida in Lord Auckland’s 
Group, lat. 503° 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 Ericacee of the Cape have in Australia a 
representative in the nearly allied Epacridacee; the 
Cactaces of America are represented by certain succulent 
forms of Mesembryanthemacez and Euphorbiaces in Africa; 
and by some Crassulacez in Europe. Trientalis europea 
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 
