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PREFACE. 



One of the most effective methods of ackliiig to the collections in 

 the National Herbarium ls for members of the scientific staff to visit 

 localities little known l>otanically and themselves make the collections 

 desired. A special advanta^^e of such fieldwoi'k lies in the opportuni- 

 ties it furnishes for makin*^^ observations cm (he native uses of plants, 

 on climatic and topographic influences in plant disti'ibution, and on 

 the innumerable other phenomena that distino-uish living from dead 

 plants^ and especially living plnnts growing in their natui'al environ- 

 ment. The botanical reports resulting from such field work are far 

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

 mens alone. 



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

 resulted in the acquisition of a valuable collection for the National 

 Herbarium and in a pul dished report. P^ach of these r(^X)rts, like the 

 accompanying one, covers only fragmentaiy poitions of his whole 

 work. All, however^ are devoted to the elucidation of the same general 

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

 valuable scries of contributions to our botanical knowledge of that 



region. 



FeEDERTCK V. COVILLE, 



Curator oftlie United States National Iltrlariun 



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