height of at least 13 feet (4 meters). A sh rub is a woody plant smaller than 

 a tree, usually with several perennial stems branching from the base. A 

 woody vine is a woody plant with the stems not erect but weak and 

 climbing or supported on other plants or objects. References on shrubs 

 commonly include woody vines, which have fewer species. 



Woody plant species are classed further as native and introduced, also 

 as wild and cultivated. A native species grows wild naturally in the 

 undisturbed vegetation. An introduced species has been brought into an 

 area by human activity, either intentionally for planting as a cultivated 

 species or accidentally as a weed. A cultivated woody species may be 

 either native to an area or introduced and may be grown for various 

 purposes. Examples are trees in plantations for wood and other forest 

 products, in orchards for fruit, and in environmental forestry plantings 

 for shade, ornament, shelterbelt, and wildlife. When it spreads from 

 cultivation, an introduced species may be designated as escaped and, 

 when common and established like wild, as naturalized. 



Botanically, woody plants are an artificial group represented among 

 many plant families. All species of woody plants native within the conti- 

 nental United States are seed plants, which are classified further as 

 gymnosperms (mostly conifers and ephedras) and flowering plants. 

 However, tree-ferns grow wild in Hawaii, Puerto Rico, and elsewhere in 

 the tropics. 



Geographical coverage. This bibliography lists general references for 

 the United States as well as those of special geographic regions and single 

 States. Publications on all 50 States, the Commonwealth of Puerto Rico, 

 the Virgin Islands, and Guam are included. Several foreign and interna- 

 tional titles have been added, where useful within the United States. 

 Likewise, some references cited may be of value in other countries, 

 where the same species may be wild or cultivated. 



Publications of local areas or parts of a State have been excluded, with 

 a few exceptions, mainly in large States. Those of National Parks have 

 been cited and listed separately (J. c. National Parks) because of the 

 special interest in these smaller preserves of natural vegetation. Geo- 

 graphical limits of each reference usually are indicated by the title or 

 subtitle. 



Pernod covered. Currently available references have been listed, those 

 containing the latest information and offered for sale or distribution. The 

 period covered is the interval from 1950 to 1975, after the superseded 

 bibliography. However, many older publications are cited. Several of 

 these contain information that has not been duplicated later for the same 

 areas. Some titles, particularly earlier ones, may be out of print but can 

 be consulted in large libraries or obtained as photocopies. Several new 

 titles of 1976 have been inserted also. 



References included. The numerous references cited in this bibliog- 

 raphy vary in size, content, and intended audience. Some are small 

 popular tree guides, handbooks, or manuals for the common species of a 



