The growth of plants. Vegetation occurs over the whole globe under the most opposite conditions. Plants flourish in the bed of the ocean as well as on land; under the extremes of cold and heat in the polar and equa-l torial regions; on the hardest rock and the soft' alluvium of the plains ; amid the snow of the mountains, in boiling springs, in dark caverns or mines. Different circumstances produce different species and genera. Absence of humidity, and extremes of temperature, are the conditions fatal to vegetable life. Trees and plants which occur in the plains dwindle with increased elevation. Plants are capable of extended naturalization, but distinct vegetable regions occur in different zones or on different heights.