128 ECONOMIC WOODS OF THE UNITED STATES 



viz., (a) a distinct central core of pith, (b) a covering of bark, and 

 between these two (c) a fairly uniform mass of wood which in- 

 creases in thickness by the addition of periodic layers on the outside. 



Some well-known representatives of the Monocotyledons are 

 the grasses (including maize, wheat, many other cereals, the bam- 

 boos, etc.), the sedges, lilies, bananas, rattans, palms, and yuccas. 

 The woody types are confined chiefly to tropical and sub-tropical 

 regions where they are extensively used but not in the form of 

 lumber. There are seven kinds of palms and nine kinds of yuccas 

 of tree size native to the United States. They are used to some 

 extent locally but as a commercial source of wood are wholly 

 negligible. 



As stated on p. 7 there are, according to Sargent's " Manual of 

 the Trees of North America," 57 families and 147 genera of Dico- 

 tyledons with representatives of tree size in this country. The 

 total number of species described is 607. Various others have 

 been introduced, mostly for decorative purposes but also to a small 

 extent for forest planting, and a few have become naturalized, bub 

 only in rare instances do their woods contribute to our commercial 

 supply. Sudworth's " Check List " * enumerates 495 trees, includ- 

 ing a few which have become thoroughly naturalized. This dis- 

 crepancy is accounted for mostly by the large number of species of 

 Cratoegus, 132 in all, described by Sargent as against 25 listed by 

 Sudworth. Not a single representative of this genus is of commer- 

 cial importance for its wood, and of the 34 species belonging to 

 the other genera of the Rosacese only one, Prunus serotina, is a 

 source of valuable lumber. One willow out of 21 species, about 20 

 oaks out of a total of 47, and about a dozen pines out of the 34 

 native to this country are commercially valuable. In the Govern- 

 ment reports on lumber production only 30 kinds are considered 

 of sufficient importance to justify separate tabulation, while about 

 20 are grouped under the single heading of "minor species." 



The following list includes the most important families and 

 genera of the Dicotyledons. Included in it are seven families 

 which are really of secondary importance so far as the amount of 

 the wood produced is concerned. These are, Aquifoliacese, 

 Bignoniaceae, Ebenacese, Hippocastanacese, Lauracese, Meliacese, 

 and Moracese. 



* Sudworth, George B.: Check last of the Forest Trees of the United 

 States, Their Names and Ranges. Bui. No. 17, U. S. Division of Forestry, 

 Washington, D. C., 1898. 



