Heilprin.] 14 [jan. 15, 



Still formed groves or thickets, they rose to a height of certainly not less 

 than 30-40 feet. Roezl, as quoted by De Candolle (Parlatore, in the " Pro- 

 dromus," xvi, ii, p. 400), and Hemslej^ give, it appears to me, too great 

 an elevation for the pines on Popocatepetl and Ixtaccihuatl, 13-14,000 

 feet ; the first figure more nearly represents the true limitation. Felix 

 and Lenk * delimit the zone on Popocatepetl at about 250 feet above the 

 ranch of Tlamacas, or, according to their statement, at almost exactly 

 13,000 feet ; my own observations place the line somewhat higher, 18,160 

 feetf — or about 100 feet lower than the point where we met with the last 

 pines on Ixtaccihuatl. 



At no other point on the earth's surface do the pines attain such an 

 extreme elevation as on the Mexican volcanoes ; indeed, if we except the 

 Juniperus fcalidmima found by Thomson in the Spiti Valley, Hima- 

 layas, at an altitude of 15,000 feet, the entire group of the Coniferae 

 almost everywhere falls far below this line. Barring exceptional cases, 

 the uppermost trees on the Himalaya, as in north temperate regions 

 generally, are conifers, but these virtually cease at an elevation of some 

 12,000 feet,:]: although flowering plants continue for still 7000 feet higher. 

 On Mt. Ararat, according to Drude, tlie uppermost trees are birches, 

 poplars and willows, and not conifers, § the tree line on the northwestern 

 face of that mountain being situated somewhat below 8400 feet. On the 

 extinct volcanic summit of the San Francisco mountain (Northcentral 

 Arizona, lat. 35° 20'), with an elevation of 12,794 feet, Hart Merriam 

 found the timber line at approximately 11,500 feet, marked by the disap- 

 pearance of the fox-tail pine (Pinus aristata) and Engelmann's spruce 

 {Pkea Engelmanni). A somewhat higher level is, perhaps, reached by 

 the balsam {Abies subalpina) in Colorado — 12,000 feet. 1| 



The point of most interest that suggests itself in connection with the 

 distribution of the Mexican pines is the distinctness of the forms from those 

 occurring in the region lying to the north. With barely an exception ^ 

 all the species occurring on the lofty volcanoes are endemic to the Mexi- 

 can (Centrali-American) region, and are consequently not found in the 

 pine tracts of the Rocky Mountain system. In view of the longitudinal 



* " Beithige ziir Geologie and Paliioutologie der Republik Mexico," p. 20, 1890. 



+ It is interesting to note in this conneclion that Von Gerolt, who made the ascent of 

 Popocatepetl in 1833, places the limit of vegetation on that mountain at 12,614 (English) 

 I'eet, not including "a mossy plant, Arenaria bryoidcs, which is occasionally found some 

 hundred feet higher." Egloffstein, " Geologj' and Physical Geography of JNIe.xico," 

 1864, p. 25. 



t Schlagintweit observed the last groups or " woods " of these trees at an elevation of 

 11,800 feet, although cultivated specimens of Populus Euphrafica, grown in the gardens 

 of the monastery of Mftngnang, were found nearly 2000 feet higher, at 13,400 feet 

 (".SItzungsber. Miinch. Akad.," 18C5, i, p. 25S). This investigator places the limit of 

 Phanerogams on the Gunshaukar Peak (lat. 31° 23', long. 80° 18') at 19,237 feet (op. c it., 

 1867, p. 516 ; also in " Results of a Scientific Mission to India and High Asia"). 



g " Handbuch der Pflanzeugeographie," p. 402. 



II C. S. Sargent, "The Woods of the United States," p. 132, 1885. 



II Pinus cembmidcs ranges into the Santa Catalina mountains of Arizona (3500 feet 

 elevation). 



