4 
THE RUBBER PLANTS OF MEXICO.* 
Until within a few years, there was but a single known source 
of commercial rubber in the entire republic of Mexico. Now 
two species are contributing regular supplies, and a third to be 
specially considered here, is likely soon to become a very im- 
portant factor in this industry. Mexico thus becomes one of the 
most important of the world’s rubber-producing countries 
other sources remain to be developed is very certain, 
since the families Euphorbiaceae, Moraceae and Apocynaceae, 
which comprise most of the rubber-yielding plants, are abun- 
dantly represented in the Mexican flora. The same may be said 
of the Sapotaceae, the family that yields gutta percha, chicle and 
balata. 
An accurate understanding of the Mexican rubber plants re- 
quires a consideration of the general climatic divisions of the 
country. Although approximately half of the republic lies within 
the tropics, geographically, this statement cannot be understood 
in a climatic sense, because most of this region is so high and 
dry that its productions range from subtropical to temperate. 
The climatically tropical region is confined to the extreme 
southern portion and strips of low land upon the Pacific and Gulf 
coasts. Over much of the southern part, where the elevation 
exceeds 3,000 feet, the climate can hardly be described as tropical, 
while even the lower portions, being exposed to strong sea- 
breezes, do not experience the torrid heat known to inland tropics. 
This region is abundantly supplied with rain. Although the rainy 
season extends only from June to November, yet the remaining 
months are by no means dry, there being normally an abundance 
of rain at all seasons. The temperature rarely falls below 70° 
or rises above 100°, some of the valleys about Vera Cruz being 
an exception, due to their peculiar location 
In this region grows the Castilla elisha the Central Amer- 
ican rubber tree, known also as the Mexican rubber tree or 
“hule,”’ in all but recent literature. So abundant is this tree 
* Abstract of a lecture delivered at the New York Botanical Garden, 
November 21, 1908. 
