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
