few days lie informed me that the mulberry-tree sap was of a milky nature, and did actually contain caoutchouc, especially on dry and bright sunny days.
With respect to the Geographical distribution of Plants, especially in its connexion with Climate, I wish to say a few words, in order to shew that the argument I after- wards draw from it, is based on a sure foundation. In repeating nearly what I have said elsewhere, I shall confine myself to the more marked differences of climate, and the vegetation it supports.
The peculiarities of the tropical zone we well know to be brightness of light, great heat, and moisture, with considerable uniformity of all throughout the year. These are all favourable to the development of vegetation, whicn is accordingly characterised by vastness ; the foliage, by richness ; and the inflorescence, by brilliancy of colouring. Hence, the proportion of trees is great, and their flowers of a size and richness which, in colder climates, are only the appanage of humbler plants ; as may be seen in the noble Amherstia, the wide-spreading Bombax, or glowing Erythrina. If we study the physiology of plants, as well as the circumstances controlling their growth, and the nature of their secretions, we find that vegetation is much affected by the different physical states of the soil and atmosphere, as well as by the supply of heat and light ; hence we may conclude, that there are different sets of plants fitted by nature for the particular circumstances in which they are to be placed. Those who have visited tropical countries, know that the position of their low and mangrove-lined coasts may be recognised by the forests of tall palms, shooting like distant masts above the surface of the sea. The very mention of the Clove, the Cinnamon, Nutmeg, Ginger, Cardamom, Plantain and Pepper recall ideas of high .temperature and rich vegetation : but these all belong to separate families of plants, as Myrtacece, c2
