DISTRIBUTION OF PLANTS IN SOUTHERN MEXICO. 429 
Altitude and Distribution of Plants in Southern Mexico. By Hans Gabow. 
M.A., Ph.D., F.R.S. (Communicated by Dr. А. В. Кехо, M.A., 
F.L.S.) 
(With two diagrams.) 
( Read 18th June, 1908.] 
Proressor A. HEILPRIN, in his very important paper, “The Temperate and 
Alpine Floras of the giant Volcanoes of Mexico" *, makes the following 
summarising statement :—“The preponderating element in the upper 
Mexican flora [from 10,000 feet upwards] 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 condition characterises the high mountain floras of tropical 
regions generally, as distinguished from those of temperate climes.” Не 
refers to Engler f as the originator of this view, and continues: “ Most of the 
Mexican plants occurring above 10,000 feet are specifically distinct from the 
congeneric forms of temperate North America, while about 10 per cent. of 
the species of high Mexican mountains are identical with those of the much 
more distant Andean summits.” 
According to Engler the alpine plants of Mexico are not connected with 
the plants of the subtropical and tropical regions of the same country, and he 
says further that, “ whilst in California and on the Rocky Mountains part of 
the alpine flora is indeed derived from that of the plains, this is not the case 
in Mexico, because there the plants of the lower regions vegetate during the 
whole year. It is impossible for them quickly to acquire an organisation 
necessary for a prolonged period of rest, or the means of protection necessary 
for defence during such a time of rest. The plants of California’s plain are 
already organised for enduring a prolonged and more or less inclement 
period, so that their descendants can gradually acquire the features necessary 
upon the new highlands.” 
These statements, probably as correct as they are ingenious, yet convey a 
somewhat erroneous impression, because they are incomplete and too general, 
If the alpine flora of a mountain in the tropics has not been derived from its 
base, it can have got to the top in two ways only—either by accident (wind, 
animals), or as a relic. The latter notion resorts, of course, to a glacial 
period as the favourite explanation ; its importance has been greatly 
exaggerated, and good instances of arctic, even subarctic, animals and plants 
as derelicts on subtropical, leave alone tropical, mountains are exceedingly 
* Proc. Amer. Phil. Soc. Philadelphia, xxx. 1892, pp. 4-22. 
+ Versuch einer Entwicklungsgeschichte der PHanzenwelt, ii. 1882. 
