PREFACE 



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

 the information 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 Crataegus which, iu the absence of sufficient information, it has been found im- 

 practicable 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 them ; 

 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 Natiirlichen Pflanzenfamilien, in which the procession is from a simpler to 

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

 Descriptions of a few species of Cratsegus are now first published; and investiga- 

 tions 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 de- 

 scribed 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 con- 

 spectus 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. Further 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 

 regions into which the country is divided according to the prevailing character of 

 the arborescent vegetation that species grows (see map forming frontispiece of the 

 volume). For example, the northeastern part of the country, including the high Ap- 

 palachian Mountains in the southern states which have chiefly a northern flora, is 

 represented by (A), and a person wishing to learn the name of a Pine-tree or of an 



