16 
phyllece, and Urnbelliferce. As elevation produces the 
same effects on temperature as increase of latitude, we find 
in the Himalayas a climate so suited to these families, 
that they form the most numerous portion of its flora. 
In company with them, also, occur some of the plants of 
China and Japan, as well as of North America ; and on 
the northern face, several of those of Siberia. Many of 
the lofty peaks being covered with snow for nine months in 
the year, which melts only when the sun has the greatest 
power, we may suppose the brightness of light in this thin 
and rarefied medium, to be an equivalent for the uninter- 
rupted sunshine of polar regions during the same months ; 
and the climate as suited to the growth of plants, which 
can scarcely be distinguished from some brought from 
Melville Island. A dwarf willow and birch, with a rhodo- 
dendron, forming the ligneous vegetation of high latitudes, 
so does a species of the first, with rhododendrons, occur at 
the highest elevations in the Himalayas, though the birch 
exists only as a tree within the limit of forest. In the same 
way that we have seen tropical families sending a few species 
into temperate climates, so do those which are character- 
istic of the latter, send their representatives into the midst 
of tropical vegetation ; but these, with the exception of the 
multiform willow, are only annuals which spring up, 
flower, and seed, during the cold-weather months in India; 
as one or two Gentians ; Anagallis, of the family of 
Primulacece ; Silene conoidea, and Saponaria Vaccaria, 
in corn-fields ; with Ranunculus sceleratus and aquatilis, 
growing in, and near water ; therefore able, from its 
equalising effects, to bear great vicissitudes of atmospheric 
temperature. 
But as these occur only in the cold-weather months, or 
from October to April, so does the cultivation in these 
months in the plains of India correspond with that of the 
