Relation of Climate tv Vegetation. 115 
The sub-tropical zone reaches from the tropics to 34° of 
lat., with a mean temperature ranging from 17°-21° C. 
We now meet with a vegetation in which evergreens pre- 
vail, and the myrtle and the laurel mark the type of the 
flora, At the same time, the high summer temperature 
induces the growth of annuals which properly belong to 
the tropical zone. 
The warm temperate zone embraces the regions between 
34° and 45° lat., with a mean temperature of 12°-17° C. 
Here we find the oak, chesnut, walnut, magnolias; while 
leguminous plants and the various grains flourish exten- 
sively. 
The cold temperate zone includes a belt lying between 
45° and 58° lat., with a temperature ranging from 6°-12° C. 
‘Here the prevailing forms of vegetation appear in the coni- 
fers, birches, maples, the heathers and junipers; while the 
rocks and trees are distinguished by an abundant growth of 
lichens, and mosses are everywhere abundant. 
The sub-arctic zone, extending from 58°-66° lat., with a 
mean temperature varying from 4°-6° C., is much more 
restricted than the former, and its limits are not always 
clearly defined. Here the pines appear only along the 
southern border, and the poplar, birch and juniper give 
character to the region. Lichens and mosses are more 
abundant. 
The Arctic region reaches from 66°-72° lat., with a mean 
temperature of about 2° C.—86° F. The prevailing tree 
here is the birch. Herbaceous plants are small, and their 
flowers disproportionately large and numerous. Lichens 
and mosses prevail, 
In the Polar zone, herbaceous plants are rare, and even 
small bushes are wanting. The surface of the earth, during 
the short season when the snow is removed, is everywhere 
characterized by the extreme poverty of its vegetation, 
seyond this is the Polar limit of perpetual snow. 
If now we return to the equator and ascend a high moun- 
tain, with increasing altitude we pass through regions 
where the vegetation successively changes, until we ulti- 
mately reach the line of perpetual snow. 
