_The Tropical Province_ (Plate III).--This is the most southern of the climatic provinces which it is convenient to recognise in North America, and includes the West Indies, Central America, and southern Mexico, together with a narrow strip on each coast of northern Mexico and the extreme southern ends of the peninsulas of Florida and of Lower California. While the land areas in this widely extended province present conspicuous differences, their climate in general is characterized by a high mean annual temperature with but moderate seasonal or daily variations, and by the occurrence in general of a wet and a dry season each year. The prevailing winds are the northeast trades. While the average yearly temperature is high, being in general about 80 deg. F., the heat in summer is less intense than in many portions of the austral provinces. In winter the temperature does not fall sufficiently to produce frost, except on the higher mountains, which, in fact, belong to one or more of the other provinces named above. On ascending the mountains a rapid change to cooler and even to frigid zones is experienced. Snow occurs on the higher portions of the mountains of Central America and Mexico, and in a few instances, as on the great volcanic cones in sight from the City of Mexico, is perennial. On the mountains just referred to all of the several climatic provinces are represented by well-characterized zones, arranged one above another, and presenting in epitome the general changes one would experience in travelling from the Gulf of Mexico to the Arctic Ocean.