PREFACE 



IN this volume I have tried to bring into convenient form for the use of students the in- 

 formation concerning the trees of North America which has been gathered at the Arnold 

 Arboretum during the last thirty years and has been largely elaborated in my Silva of 

 North America. 



The indigenous trees of no other region of equal extent are, perhaps, so well known as 

 those that grow naturally in North America. There is, however, still much to be learned 

 about them. In the southern states, one of the most remarkable extratropical regions in 

 the world in the richness of its arborescent flora, several species are still imperfectly known, 

 while it is not improbable that a few may have escaped entirely the notice of botanists; and 

 in the northern states are several forms of Cratsegus which, in the absence of sufficient in- 

 formation, it has been found impracticable to include in this volume. Little is known as 

 yet of the silvicultural value and requirements of North American trees, or of the diseases 

 that affect ihem; and one of the objects of this volume is to stimulate further investigation 

 of their characters and needs. 



The arrangement of families and genera adopted in this volume is that of Engler & 

 Prantl's Die Naturlichen Pflanzenfamilien, in which the procession is from a simpler to a 

 more complex structure. The nomenclature is that of The Silva of North America. De- 

 scriptions of a few species of Crataegus are now first published, and investigations made 

 since the publication of the last volume of The Silva of North America, in December, 1902, 

 have necessitated the introduction of a few additional trees described by other authors, and 

 occasional changes of names. 



An analytical key to the families, based on the arrangement and character of the leaves, 

 will lead the reader first to the family to which any tree belongs; a conspectus of the genera, 

 embodying the important and easily discovered contrasting characters of each genus and 

 following the description of each family represented by more than one genus, will lead him 

 to the genus he is trying to determine; and a similar conspectus of the species, following the 

 description of the genus, will finally bring him to the species for which he is looking. Fur- 

 ther to facilitate the determination, one or more letters, attached to the name of the species 

 in the conspectus following the description of the genus, indicate in which of the eight re- 

 gions into which the country is divided according to the prevailing character of the arbores- 

 cent vegetation that species grows (see map forming frontispiece of the volume). For 

 example, the northeastern part of the country, including the high Appalachian Mountains 

 in the southern states which have chiefly a northern flora, is represented by (A), and a per- 

 son wishing to learn the name of a Pine-tree or of an Oak in that region need occupy him- 

 self only with those species which in the conspectus of the genus Quercus or Pinus are 

 followed by the letter (A), while a person wishing to determine an Oak or a Pine-tree in 

 Oregon or California may pass over all species which are not followed by (G), the letter 

 which represents the Pacific coast region south of the state of Washington. 



The sign of degrees () is used in this work to represent feet, and the sign of minutes (') 

 inches. 



The illustrations which accompany each species and important variety are one half the 

 size of nature, except in the case of a few of the large Pine cones, the flowers of some of the 



