Heilprin.] ^^ [Jan. 15, 



luxuriant forests of the eastern tierra caliente, it presents an unbroken 

 botanical front to the line of perpetual snow, 15,000 feet above the sea, and 

 thus exhibits in beautiful sequence the different vegetal zones which 

 climate more particularly has marked out. There is probably no other 

 mountain in the world which so thoroughly presents the essentials of a 

 study of mountain floras as Orizaba ; the luxuriance of growth at its base, 

 the high level to which the forest zone attains, and the isolation, due to 

 volcanic structure, of the peak itself, are the specially distinguishing fea- 

 tures of tiiis summit. So far as the temperate and alpine floras of the other 

 giant mountains of Mexico are concerned — Popocatepetl, Ixtaccihuatl and 

 the Nevado de Toluca — there is no question that they are very closely 

 related to the similar floras of the Star Mountain, as indeed it would 

 naturally be expected they would be. Of this correspondence I have 

 satisfied myself through a personal examination of the floras in situ ; un- 

 fortunately, the conditions attending the ascent of these mountains were 

 such as to prevent us from making more than "sample " collections, but 

 they illustrate in a broad way the general features of the vegetation. All 

 four summits rise from the table land through a zone of pine forest. On 

 the western slope of Orizaba, or towards the town of San Andres Chalchi- 

 coraula, we found the pines, with Pinus Montezumce (var. macrophylla — 

 the common long-leaved species), P. Teocote and P. pseudostrohus, to 

 begin as a distinct zone, at an elevation of some 9000 feet, occupying 

 nearly the same position on the western slopes of Popocatepetl and 

 Toluca ; on Ixtaccihuatl the line descends approximately 500 feet lower. 

 There can be little question, it appears to me, that the limitation down- 

 ward in these special cases is not so much dependent upon climatic con- 

 ditions as it is upon certain physical peculiarities of the surroundings and 

 the artificial means that have been resorted to for the removal of the 

 native growth. The vast accumulation of ash and dust-sand which 

 to-day envelopes the plateau base of the mountain, deposited as a disinte- 

 gration downw^ash from above or as a wind sediment from below, lends 

 itself at best to the development of but a scant vegetation ; large areas are 

 Avholly barren, while others are redeemed only by a withered and scattered 

 growth of grass and insignificant herbs. Over these lower areas trees are 

 but distant ornaments. That this limitation of 9000 feet is not the actual 

 or natural boundary of the pine zone is shown by the condition of the 

 eastern face of the mountain, which descends from the plateau, or by the 

 face of the plateau itself. Thus, on the hills about the town of Orizaba, 

 at an elevation of some 4800 feet, we observed Pinus pseudostrohus — a form 

 closely related to P. Montezuma, and also entering into the composition of 

 the lower pine woods of the Citlaltepetl — growing in great profusion ; and 

 on tlie steep southern face of tlie plateau descending to the volcano of 

 Jorullo, we followed Pinus MoutezicmcB or P. occidentalis to the level of 

 4000 feet, or perhaps even lower — far below the upper level wiiich the 

 palms attain in certain parts of Mexico.* 



* We observed a palmetto-like form, probably a Brahea, growing abundantly ou the 



