PREFACE. 



One of the mosl effective methods of adding to the collections in 

 the National Herbarium is foi members of the scientific staff to visit 

 localities little known botanically and themselves make the collections 

 desired. A special advantage of such fieldwork lies in the opportuni- 

 ties it furnishes for making observations on the native uses of plants, 

 on climatic and topographic influences in plant distribution, and on 

 the innumerable other phenomena that distinguish living from dead 

 plants, and especially living plants growing in their natural environ- 

 ment. The botanical reports resulting from such fieldwork arc Par 

 more critical and more valuable than those based on herbarium speci- 

 mens alone. 



Doctor Rose has made five journeys to Mexico, each of which has 

 resulted in the acquisition of a valuable collection for the National 

 Herbarium and in a published report. Each of these reports, like the 

 accompanying one. covers only fragmentary portions of his whole 

 work. All. however, are devoted to the elucidation <»! the same general 

 subject, the flora of central .Mexico, and together they form a highly 

 valuable series of contributions to our botanical knowledge of that 

 region. 



Frederick V. ( '< >\ elle, 

 Curator of the United States National Herbarium. 





