2 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



mercial inipoitanco. In the immense mountain ranges there are 

 hundreds of difficult peaks and almost inaccessible canyons whose ex- 

 ploration is extremely tedious: in the south the tropical forests are 

 penetrated with difficulty, and the lofty branches of their trees are 

 almost inaccessible to the collector; a^vay from the Sierra Madre are 

 innumerable isolated masses of mountains and hills, still unvisited 

 by a botanist, which must yield a host of localized species. Con- 

 sider, in addition, the fact that Mexico is still very imperfectly sup- 

 plied with transportation facilities and it becomes evident that many 

 years must elapse before a comprehensive knowledge of the flora is 

 possible. 



It is unfortunate, and at the same time remarkable, that no flora 

 of any part of tropical continental North America has ever been pre- 

 pared. Indeed, in this respect all of North xVmerica has made little 

 progress as compared with Europe, some parts of Asia. Australia, 

 and Africa, or even South America. The flora of tropical Africa, 

 the most recent of all the great regions of the earth to be explored by 

 European peoples, has been adequately treated in botanical litera- 

 ture; and the flora of Brazil has been described in a monumental 

 series of volumes, of which any country might well be proud, but 

 whose equal no other country possesses. For no political unit of 

 North America has a modern descriptive or even a synoptical flora 

 ever been published. 



The only publication approaching a flora of Mexico which has 

 ever been completed is the Botany of the Biologia Centrali-Ameri- 

 cana, compiled by Hemsley and issued from 1879 to 1888. This, 

 though including no descriptive notes (except incidentally) nor any 

 means of identifying the species, is a comprehensive work, listing all 

 the species of the higher plants known at that time from Mexico 

 (excluding Baja California) and Central America. Ranges and 

 definite localities are given for all the species, together with the more 

 important synonj^mj'. It is superflous to state that after almost 40 

 years this work has lost much of its former usefulness, as a result 

 of recent botanical discoveries. Nevertheless the five volumes of the' 

 Biologia will always remain an invaluable and classic work upon 

 tropical American plants. 



Botanical cxjiloration in Mexico has now progressed to the point 

 where a descriptive flora of the region is jn-acticablc, and such a com- 

 pilation is urgently needed. The work here offered is intended to in- 

 clude a complete list of the woody plants known from Mexico, with 

 keys for their determination. This arbitrary and artificial division 

 of the Mexican flora was chosen for treatment because it contains 

 those species which are the most conspicuous elements of the vegeta- 

 tion, as well as those which are of most importance from an economic 

 standpoint. It includes, moreover, the larger portion of ihe Mexican 



