PREFACE. 



THIS manual is intended to do for its own range what has 

 been for a long time so admirably done for the Northeastern 

 States by Dr. Gray's Manual. About ten years ago it was the 

 writer's privilege to assist Professor Porter in the preparation 

 of the Synopsis of the Flora of Colorado, a first attempt to bring 

 together in convenient shape, for a restricted region, the scat- 

 tered material of our Western collectors. The demand even 

 then for a book by no means complete or conveniently arranged 

 was unexpected, and in the wonderful development of the 

 decade since then lies the confidence that a more convenient 

 book covering a greater range will be welcome to many. The 

 difficulties attending the naming of Western plants, owing to 

 the fact that descriptions are scattered through numerous and 

 often inaccessible publications, can only be appreciated by 

 those who have attempted it. From this fact, a great stimulus 

 to the study of systematic botany has been lacking, collectors 

 have been almost entirely professional, and a thousand possible 

 streams of information have been reduced to a score. 



West of the Mississippi Valley prairie region, which is but 

 the continuation of more eastern conditions, there are three 

 well-defined floras. One is that of the Pacific slope ; another 

 is Mexican in character, extending from the Great Basin to 

 Arizona, New Mexico, Western Texas, and southward into 

 Mexico ; the third is the Rocky Mountain region, extending 

 eastward across the plains to the prairies. 



The first region is well provided for in the two volumes of 

 the Botany of California. The second, in the Great Basin, has 



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