CHECK LIST OF FOREST TREES 11 



in its distribution, but known to be arborescent in North America 

 only in a few counties of southern Illinois. Another example is that 

 of the Buttonbush (Cephalanthus occidentalis Linnaeus), which was 

 long known only as a thicket-forming shrub, but which comparatively 

 recently was found to become a small tree in southern Michigan, 

 southern Arkansas, eastern Texas, and at a few stations in California. 

 Still another example is the California Redbud (Cercis occidentalis 

 Torrey). It is commonly a low-spreading shrub. Occasionally, 

 however, examples have been found 12 or 15 feet high and 4 or 5 

 inches in diameter, and recently J. D. Coffman. of the Forest Service, 

 found a tree of this species in California 13 J^ inches in diameter and 

 25 feet high. All such potentially arborescent species have been 

 freely admitted to our tree flora. 



RANGE OF NEWLY-DESCRIBED AND LITTLE-KNOWN TREES 



Because a considerable number of the trees now listed are newly 

 described species or varieties, there is but little information of record 

 regarding tneir ranges and much of what is known represents records 

 only of localities from which specimens have been collected. It is 

 to be expected that later field studies will unite the scattered stations 

 now known into consistently connected ranges. But it is only 

 through the assistance of many observers that this desirable informa- 

 tion can be obtained. 



NATURE OF THIS WORK 



In preparing this revision of the Check List the author can claim 

 little originality. Such a work represents rather the bringing to- 

 gether in catalogue form for convenient reference what collectively a 

 large number of different writers and observers have made available. 

 He has, of course, used his own judgment in accepting the opinions 

 of others regarding the standing of the many species and varieties 

 that have been published. In matters of this sort complete agree- 

 ment is perhaps impossible, since the knowledge and the point of 

 view of every one who writes about trees are necessarily different. 

 Perhaps, however, agreement as to whether a tree should be rated as 

 a species or as a variety is unimportant, the more essential point 

 being that the plant be named and clearly distinguished, either as a 

 variety or species. Singularly enough, authors sometimes fail to 

 agree with themselves for long, obviously because increased knowl- 

 edge of a tree, already named, may necessitate a change of judgment 

 from a previous decision regarding its rank. 



ACKNOWLEDGMENTS 



In collecting the information used in this revision, the author has 

 found it very difficult to acknowledge all of the many sources from 

 which it has been drawn. So far as possible, however, credit has been 

 given in the proper place. 



In this connection the writer desires to express his grateful appre- 

 ciation for the cordial and helpful cooperation received from mem- 

 bers of the Forest Service who have contributed much valuable 

 information regarding the exact range of forest trees observed within 

 the national forests. Particular reference is made here of notes 

 compiled by H. G. Calkins on the range of trees in the Coronado 

 National Forest, Arizona, and placed at the author's disposal through 



