THE FLORA OF NORTH MEXICO. 143 



or sometimes a little later ; from Mazatlan northward to the river Colorado, a country 

 situated immediately without the tropics, the equinoctial seasons are less distinctly 

 marked, the climate partaking more of the character of that of the temperate zone, and 

 being besides very dry. In the mountains every altitude has its own range of tempe- 

 rature and moisture; the western declivity, however, possessing generally a higher 

 temperature and a greater degree of moisture than the eastern. On the higher summits 

 the rivulets are frozen during the cold season, and snow often falls. 



" The climate of the tableland of Durango and Chihuahua is like that of the greatest 

 portion of the elevated plains of Mexico, dry, differing in that respect essentially 

 from that of the higher regions of the Colombian, Ecuadorian, and Peruvian Andes, 

 where moisture is abundant, and brooks, rivers, lagoons, and lakes promote a more 

 luxuriant vegetation than is to be met with in Mexico at similar elevations. The 

 extremes of heat and cold are unknown. Towards the end of February the night-frosts 

 cease ; spring commences, poplars and willows begin to get green, peaches and apricots 

 put forth their blossoms, but the temperature alone, though fast increasing during 

 April and May, is not sufficient to awaken nature altogether. The fields remain dry, 

 until towards the latter end of May, or in the beginning of June, the vivifying rains 

 set in ; in a few days every herb, every shrub, and tree has started into life, and the 

 vegetation develops itself with great rapidity : the season answering to the North- 

 European spring has commenced. Early in September the rains cease ; in October the 

 night-frosts (which last until February) recommence, except which there are few 

 indications of winter ; snow seldom falls, and never remains long on the ground. The 

 great aridity of the climate is best illustrated by the fact that, although the rainy 

 season only terminates early in September, there is very little water to be met with in 

 any part of the plains during the winter months (October until February). The 

 periodical streams seem to disappear at the moment the rains themselves cease, and 

 the perpetual springs, streams, and small rivers are so few in number that the traveller 

 has very often to search for hours ere he is able to meet with water ; fortunately the 

 Mexican flora mostly has furnished a guide to places where there is always a good 

 supply by planting on the banks of the running streams Sabino trees (Taxodium 

 distichum), to inform the weary traveller, when he descries their high waving tops, 

 that the object of his search is close at hand. 



" The immediate neighbourhood of the coast is generally lined with a dull maritime 

 vegetation, the Mangrove tree being very frequent, and appearing from Acapulco to a 

 little to the north of Mazatlan (lat. 24° 38' N.), where, together with the Cocoa-nut 

 Palm and many other forms common all along the western shores of America, from 

 Guayaquil northwards, it reaches its extreme northern limit. Advancing a short 

 distance inland, the aspect of the vegetation improves, trees of Crescentia alata, llama- 

 toxylon campechianum, Cordia gerascanthus, Ipomcea arborescens, Cratceva tapia, 

 evergreen Figs, and feathery Mimosas, shrubs of Bixa orellana, Malvaviscus arboreus, 



