1 n; 



1892.] -»•'-' [Ilcilprin. 



direction of tliese mountains and the fact that they are continued by a 

 plateau system of elevations of from 6000-8000 feet into the very heart of 

 the volcanic area, this circumstance appears a little remarkable ; its 

 explanation is possibly to be sought in the same series of conditions which 

 have determined the endemic character of the alpine flora generally of 

 the Mexican and South American summits. In the case of such hardy 

 perennials as the pines, however, it is more difBcult to account for the 

 anomaly than in that of the seemingly much more pliable herbaceous 

 plants, which are commonly assumed to lend themselves more readily 

 to changes or modifications as the result of alterations in the physical 

 conditions of their surroundings. The comparatively recent origin of 

 the jNIexican volcanoes proves that the floras which they carry must be of 

 equally recent date ; it follows, therefore, as a corollary that if the com- 

 ponents of these floras are derivatives from preexisting floras still extant, 

 such modifications of structure as they have undergone must have been 

 rapid in their formation — more rapid, probably, than is generally allowed 

 for modifications of this kind. Can it, perhaps, be assumed that the 

 special cbaiacteristics and conditions which belong to elevated volcanic 

 cones are conducive to rapid change? It is true that not all the volcanic 

 summits of Mexico are of equivalent age, and it can probably be assumed 

 that some are of even considerably greater age than others (although 

 possibly belonging to the same period of geological time); thus the 

 worn-off" and efiiiced summit of the Ixtaccihuatl, without doubt, long 

 antedates such perfect cones as Orizaba and Popocatepetl; and the 

 serrated ridges of the Ajusco, or their continuations, bear a similar rela- 

 tion to the series of more or less perfect cones and bosses which are 

 distributed over the plateau north of the line occupied by them. Possibly 

 the existing flora was first developed on such ancient slopes, whence by a 

 gradual transference it gained the position which it now holds (largely 

 modified and altered in form). 



It must be admitted, however, that our knowledge on these points is 

 still so limited that it can scarcely originate more than speculation or 

 surmise ; it no more explains the present problem than it answers the 

 question: Why are the pines limited to the northern hemisphere — or 

 more definitely, why the North American pines cease so abruptly in 

 Nicaragua '? What are the special conditions which prevent them from 

 spreading further southward, and why is the upper zone of the Andes 

 destitute of these trees? Indeed, the endemic character of the Mexican 

 conifers and the absence of their immediate representative in South 

 America miglit suggest to some an origination wholly independent of a 

 true North American stock — an origination suggestive of a former Atlantis. 

 The presence of pines in some of the West Indian islands — Cuba, Jamaica, 

 Santo Domingo, and again in the Canary Islands* — might, moreover, be 

 taken in evidence of a trans-Atlantic land connection having actually 



* Piiius Canaricnsis, the last of the three-leaved pines from the western region of the 

 Old World. 



