304 Part III. Chapter 3. 
been continuous. The composition of the flora of Costa Rica ') and Panama, so 
far as investigated is decidediy South American. Taking some of the mainly 
tropic orders, such as Dilleniaceae and Anonaceae, we note a gradual thinning 
out northward, and an extension into the southern province of many South 
American species. The essentially eastern South American Lecythideae is 
represented by four genera and seven species, one of which is common in 
Nicaragua, the northern limit of these trees. Fodocarpus replaces Pinus in the 
mountains of Costa Rica extending to Cuba in two species: P. angustifola, 
P. aristulata, and to Jamaica in ?. Urbanii and P. Purdicana (see colored 
map), and the Cylanthaceae are relatively numerous in the lower regions. Note- 
worthy examples of southern limits of northern types are offered by Ziguidambar, 
Sabiaceae and Fuglandaceae in Costa Rica, and Pinus in northern Nicaragua. 
The oak-vegetation of Volcan de Chiriqui comprises at least three species; 
and Arbutus and Arctostaphylos give way to South American genera of the 
Vacciniaceae in the mountains generally. Chiamaedorea, the characteristic genus 
- of palms in the oak forests of south Mexico, is represented in the southern 
province by at least half ä dozen species, but the majority of palms belong to 
genera having their greatest development south of Panama, as is excellentiy 
exemplified by the genus Aszalea (Honduras-palm, Attalea Cohune, Plate V), 
which is found through the whole of Brazil extending, as far, as Guiana ar 
Colombia, and next to Cocos is a prevailing genus of brazilian palms. Many 
other examples of a change in the vegetation nearly coincident with the 
northern boundary of Nicaragua might be given. 
Nearly, if not quite, all of the genera of the mountain flora there recorded 
from 8000 feet and upwards in our southern province are such as range from 
Mexico to the Andes of South America and some of them farther. The 
alpine forms of the Andes of South America belong for the greater part to ur 
same genera which inhabit the higher regions of the mountains of Central 
America and Mexico, though the species are rarely identical. There seems 
to have been an northward extension of temperate and alpine forms, 2 
well, as tropic, and such genera as Drimys, Fuchsia, Colobanthus, Calceolarıa, 
Roupala, etc. are perhaps of southern origin. It follows that northern Mexico 
is the focus of a xerophilous flora extending into the dry regions of South 
Mexico, and into territories north of Mexico. The central province, disregarding 
the purely tropic and the xerophilous overlappings, is a mingling of northern 
and ‚southern types which exhibit an extraordinarily rich production of local 
species, associated with about ı2 per cent of indigenous genera°). The 
southern region is an outlying portion of.the American tropic flora, and ! 
composition is almost limited to specific differentiations. The tropic element 
in this region is more closely allied to that of eastern South America, eVet 
ı) PoLAKowsKY, H.: Die Pflanzenwelt von Costa Rica. XVI. Jahresbericht des Vereins für 
Erdkunde zu Dresden. 1879: 25—ı124. 
2) HEusLeEY, l.c. 
