PREFACE. 



cies may be understood as found more or less generally through- 

 out the whole area, or at least to near the western limits. 



KoMExcLATURE, AccEXTUATiox OF Xames, etc. — In case 

 of question respecting the proper name to be adopted for any 

 species, Dr. Gray's known and expressed views have been fol- 

 lowed, it is believed, throughout the work. While reasonable 

 regard has been paid to the claims of priority, the purpose has 

 been to avoid unnecessary changes, in the belief that such 

 changes are in most cases an unmitigated evil. Synonyms are 

 rarely given except where changes have been made. As a guide 

 to correct pronunciation, the long sound of the accented vow^el 

 (modified often in personal names) is indicated, as heretofore, 

 by the grave accent (^), and the short sound by the acute ('). 

 In regard to the derivations of generic names, many valuable 

 suggestions have been due to W. E. Gerard, Esq., of oS^ew York. 



Promixext Characters are indicated by the use of IUiIIg 

 type for the leading distinctions of the Orders, and generally 

 in the specific descriptions for those points by which two or 

 more nearly allied species may be most readily distinguished. 

 The ready discrimination of the genera is provided for by a 

 Synopsis of their leading characters under each order. When- 

 ever a genus comprises several species, pains have been taken 

 to render important differences conspicuous by proper group- 

 ing, and when needed b}^ a series of subordinate divisions and 

 subdivisions. The headings of these various groups are to be 

 considered as belonging to and forming a part of the specific 

 characters of the several species under them, — a fact which 

 the student should always bear in mind. 



Arraxgemext of the Orders. — The iSTatural Orders are 

 disposed in very close accordance w^th the method followed 

 by Bentham and Hooker in the Genera Plantaruvi, the princi- 

 ples of w^hich are concisely shown in the Synopsis of Orders 

 which precedes the Analytical Key. The GymnospermcB are 

 retained as a Subclass following the Angiospermous Dicotyle- 

 dons, with which they have an obvious relationship, in pref- 

 erence to placing them, as some authorities would do, next 

 before the Pteridophytes. to which their affinity, if no less 

 certain, is nevertheless obscure. A more natural arrange- 

 ment than either would be the withdrawal of the Endogens, 

 placing them at the beginning, in perhaps an inverse order. 



