PREFACE 



In bringing Dr. Asa Gray's well-known Manual to date and inte 

 accord with, modern' views of classification and nomenclature, the 

 present editors have lound it necessary to rearrange it throughout, 

 rewrite considerable portions, modify at least slightly nearly all the 

 descriptions, and adopt certain principles of nomenclature (notably 

 the one relating to the first specific name) somewhat at variance with 

 Dr. Gray's practice. Although these changes have been numerous 

 and in some respects fundamental, it is believed that they are all in 

 thorough accord with the liberal spirit of progress which character- 

 ized his own successive publications. Wherever possible and in all 

 cases of doubt, the wording of the sixth edition, prepared by Dr. 

 Serexo Watson and Professor John Merle Coulter, and pub- 

 lished in January, 1890, has been retained. 



In the arrangement of the plant-families and in grouping them 

 in orders, the admirable system of Eichler, in recent years much 

 elaborated and perfected by Engler and Prantl, has been followed 

 with a few deviations of minor importance. 



The term order, used by Dr. Gray as synonymous with family, is 

 here employed, according to the recommendation of the International 

 Botanical Congress at Vienna, to designate a group of superior rank ; 

 the same, in fact, which has sometimes been called a cohort. Orders, 

 in this sense, are not capable of sharp definition in the manner of 

 species, genera, or even families, nor. is it to be supposed that one 

 order begins in development where the preceding ends. They are 

 rather to be conceived as representing somewhat parallel and long- 

 disconnected lines or tendencies in evolutionary development. The 

 groux^ing of the families into orders is shown in the tabular view on 

 pages 23-27. 



To cover a more natural floral area and to make the Manual con- 

 venient for a greater number of users, some alterations have been 

 made in the geographic limits adopted in the sixth edition. These 

 changes result in (1) the exclusion of the territory at the west between 

 the 96th and 100th meridians, a region now known to include a con- 



5 



