1S92.J -^1 [Heilprln. 



Anionc; the more distinctive vegetal features of the lower volcanic slopes 

 may be cited the dense bushes or thickets of Arbutns spinulosa and (the 

 rigid) Symphoricarpnsmicrophyllu!^, which border the rough mule-ways for 

 long distances at (approximately) the 11,000 foot level, characterizing there 

 a partial zone of their own. "We found the ericaceous plants particularly 

 abundant on Popocatepetl. With them is associated the magnificent red- 

 flowering honeysuckle (Lonicerajilosa), a stately plant 4-6 feet in height, 

 which is certainly one of the most attractive growths of the region. To 

 this zone succeeds a belt of composites, characterized by a special devel- 

 opment of BaccJiaris concaoa and Erigeron fnaximus. It need hardly be 

 said that the zonal lines — if, indeed, they are really worthy of such char- 

 acterization — are not well differentiated ; the plants of different belts mix 

 in well with one another, so that everywhere there is considerable overlap. 

 Nor do the same plants always occupy the same positions on the different 

 mountains. Still, an approximation to zonal separation is to an extent 

 manifest, especially where the maximal development of any series of 

 plants is reached. 



One of the most beautiful plants of the roadside, most abundant, per- 

 haps, between 11,000 and 12,000 feet, is a pink evening primrose (prob- 

 ably (Eiiothera tetraptera) with flowers somewhat smaller than those of a 

 rose; the plant can, indeed, be appropriately designated the "alpine 

 rose" of the Mexican mountains, as it is not unlike in general appearance 

 a wild rose, though provided with only four petals. Its showy blossoms 

 constitute one of the glories of the mountain roadways, but it is not 

 entirely absent from favored open spots of the low^er regions. "We met 

 with the plant abundantly in the meadows about Patzcuaro, at an eleva- 

 tion barely exceeding 7000 feet. Here it was associated with Jussieua 

 repens, Guphea procumbens, Sisyrmchium micranthum (J), BaccJiaris con- 

 ferta, etc. 



The preponderating element in the upper Mexican flora is made up of 

 forms which distinctly represent the temperate and Arctic regions, and 

 not of modifications (suited to a more rigorous climate) of the lower or 

 basal floras of the same region. This is the condition which is found to 

 characterize the high mountain floras of tropical regions generally, as 

 distinguished from those of temperate climes, and for reasons which have 

 been well pointed out by Engler in his exhaustive treatment on the devel- 

 opment of the vegetable world.* Most of the Mexican plants occurring 

 above 10,000 feet, while they are to a very great extent congeneric with 

 the forms of temperate North America, are specifically almost wholly dis- 

 tinct. Indeed, the relationship with the plants of the much more distant 

 Andean summits, so far as the recurrence of identical specific forms is 

 concerned, appears to be considerably more intimate than it is with the 

 forms belonging to the north. The reason for this is to me at the present 

 time entirely conjectural. 



* " Versuch einer Entwickelungsgeschichte der Pflanzenwelt," ii, 18S2. 



