other scrubland acacias give way to related species and grow 

 taller, and palms appear. Many of the broad-leafed woody plants 

 that were mere shrubs In the chaparral blossom forth as real 

 trees, and in a matter of miles narrow gallery forests appear 

 along waterways. At the same time, since one is going steadily 

 southward, the belts we have left behind rise up the mountain 

 sides, and beneath them wedges of tropical growth begin to slip 

 in. This is the nature of the whole southern Sierra Madre Orien- 

 tal, which culminates in a montane facies of the true equatorial 

 forests in the gorges between those ranges just a little south of 

 the twenty-second parallel. 



THE TROPICS 



1 have never been able to fathom just why the regions of the 

 world between the tropics and the polar circles are called the 

 "temperate" zones. By comparison with other regions, they are 

 the most intemperate, having just as widely fluctuating over-all 

 climates as the polar regions and a much greater inclination to 

 sudden changes in short-term weather than the tropics. Contrary 

 to popular opinion, it is rarely if ever too hot in the tropics; the 

 regions of great heat lie in the desert belts to north and south, 

 while over considerable areas in the tropics it can often be much 

 loo cold for comfort. Further, high humidity is not unhealthy 

 nor. except psychologically (or unless one must wear unsuitable 

 clothes and work in buildings designed for sub-Arctic winters), is 

 it really uncomfortable. Much more uncomfortable is the desic- 

 cating effect of the super-dry atmosphere of deserts, which cracks 

 your lips, makes you gasp, irritates your skin, and lays you open 

 to heat prostration. In the tropics the equal length of day and 

 night throughout the year acts as a powerful factor in tempering 

 the more violent variations of over-all climate, so that even in 

 areas of great natural turbulence the weather tends, on the 

 whole, to be equable; while both the seasonal and daily ranges 

 of temperature are very modest compared to those of the so- 

 called temperate and polar regions. 



A certain mellowing, or perhaps one might better say amel- 

 ioration, of the climate to which northerners are accustomed is 

 noticeable in the southeast of this country, in Florida and other 

 Gulf states, and in southern California, especially in winter. The 

 difference is sometimes quite noticeable as far north, for in- 

 stance, as the mouth of the Susquehanna River, where there is 

 almost invariably a "change in climate." But this is as nothing 

 to that which takes place when one enters the true tropics. 



The earth is girdled by a wide equatorial or tropical belt, 

 outside which, to north and south, lie the two "temperate" belts; 

 while it is capped, top and bottom, by two circular polar areas. 

 Between the tropics and the temperate belts lie the imaginary 

 lines called the Tropic of Cancer and the Tropic of Capricorn. 

 These lines represent the points farthest north and south above 

 which the sun is at some time in the year directly vertical. The 

 Arctic and Antarctic Circles represent the lines farthest from the 

 poles at which the sun disappears completely for at least one day 

 per year. These conditions are due to the tilt of the earth at 

 23 degrees to the plane of its travel around the sun. These 

 divisions, although not marked by neat lines on the earth's 

 surface — except by thoughtful governments such as the Mexi- 

 can — are, moreover, real change-over points for many features 

 of the earth's surface; and, notably, its vegetation. Even when 

 the major belts have been pushed far to the north or south by 

 other factors, marked changes invariably occur as you cross any 

 of these empirical lines. 



In Mexico these changes are quite startling, because on the 



narrow coastal belts everything seems suddenly to be dlflcrcnt. 

 To the north side the land is still typically "northern"; lo the 

 south it is almost aggressively tropical. 



THE TROPICALES 



When it comes to vegetation, even of a most abstruse nature, the 

 Mexicans almost invariably have, as I have already hinted, "a 

 word for it." All over this province you will hear about the 

 Iropicales. Finding himself already in a country choked with 

 palms, parrots, and bananas, the average traveler becomes con- 

 siderably confused about this when he is told, often with a 

 knowing wag of the head, that he should visit the areas so 

 named. The fact is that the Mexicans have no such misconcep- 

 tions about the tropics as we have. 



Not a few visitors to the Florida Everglades come away with 

 the impression that they have visited the tropics, and even text- 

 books sometimes still refer to the Gulf coasts as being "sub- 

 tropical." Tourists getting sufficiently far south of the border to 

 be out of the Desert Belt are sometimes convinced that they have 

 entered the "jungle," as it is popularly called, and that they are 

 in the periphery of a land of mighty forests. They do not usually 

 know that they will not reach the true tropics till they pass south 

 of the tenth parallel, or that both the equatorial and the sub- 

 tropical regions are just as varied as the temperate, and divided 

 into as many major belts and subdivisions. The Mexicans know 

 otherwise, and they have for centuries appreciated the im- 

 portance and influence of the mountains on these and other 

 types of vegetation. They make a clear distinction between the 

 two truly tropical types of forest and all others, and they col- 

 lectively call the former the tropicales. 



The best way to visit these is by means of a number of little 

 roads that now push into the Sierra Madre Oriental from the 

 eastern coastal plain. By one of these — that goes due west into 

 the mountains a little south of the Tropic of Cancer — you go 

 straight up and over five ranges to a small town named Ciudad 

 del Mais and, some ten miles beyond this, you come to the divide 

 or watershed leading down onto the central plateau. By following 

 this route you may. in a distance of only forty miles as the crow 

 flies, inspect the whole northern part of the eastern Sierra 

 complex. 



The first range is clothed on its east face with a very peculiar 

 growth of assorted deciduous trees and some palms. Its west side 

 is much more arid and has many cactuses. The valley beyond 

 (the one containing a place called Nuevo Morales) is however 

 fully tropical, with many large trees, considerable groves of tall 

 palms, and a special type of white-headed cactus. The next range 

 is clothed on both faces with lush tropicale. with many palms 

 in the gulleys and a mixture of deciduous and evergreen trees 

 loaded with bromeliads. other epiphytic plants, and vines. Large- 

 leafed herbs gather in the moister corners where there is deep 

 shade. This growth leads down onto a second valley (that of 

 El Naranjo). which is a well-watered flood plain dotted with tall 

 palms and clumps of deciduous trees of small stature but mostly 

 of true tropical forms. 



The feet of the next range, the third one from the coast, are 

 clothed in an almost solid stand of tall Cabbage and other palms 

 intermingled with the beautiful coppery-barked Madrone tree. 

 But. as you go up the east face, you first enter and then continue 

 upward for two thousand feet through a mixed deciduous and 

 evergreen tropicale. positively choked underneath its canopy 

 with a riot of broad-leafed small trees and shrubs and giant 

 herbs with vast fleshy leaves. This, however, is the end of the 



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