APPENDIX 



The Woods of the United States 



Wood of economic importance is obtained from certain repre- 

 sentatives of the. higiiest sub-division of the plant world — the 

 Spermatophytes or true flowering and seed-bearing plants. Bot- 

 anists separate this large group, chiefly on the basis of floral and 

 fruit characters, into two classes, viz., the Gymnosperms and the 

 Angiosperms. 



The Gymnosperms are all woody plants, either trees or shrubs. 

 Of the fifteen genera indigenous to the United States, two (Taxus 

 and Tumion or Torreya) belong to the Taxacege or yew family and 

 are of little or no commercial importance. The other thirteen 

 belong to the Coniferae or true cone-bearers. 



The woods of the Coniferae, commonly known as coniferous 

 woods or softwoods, are esteemed for structural purposes because 

 they combine a high degree of strength and stiffness with com- 

 paratively light weight and ease of manipulation. They are 

 separable into (a) the pine-like and (6) the cedar-like. The first 

 includes the pines (Pinus), Douglas fir (Pseudotsuga), spruces 

 (Picea), larches (Larix), true firs (Abies), and the hemlocks (Tsuga). 

 The second group embraces the junipers (Juniperus), various 

 cedars {Chamcecyparis, Thuya, Libocedrus), the cypresses (Cupres- 

 siis and Taxodium), and the sequoias (Sequoia). The cedar-like 

 woods are characterized by their resistance to decay and also, with 

 the exception of Taxodium and Sequoia, by their fragrant scent. 



The Angiosperms are very abundantly represented in the flora 

 of this country and include a large proportion of herbaceous forms. 

 Two sub-classes are recognized, viz., the Monocotyledons and the 

 Dicotyledons, referring to the number of cotyledons or seed-leaves 

 of the embryo. There are also fundamental differences in their 

 stem structures. 



Monocotyledonous stems are mostly unbranched and the wood 

 is confined to isolated strands disposed irregularly in a mass of 

 softer tissue, becoming more and more compact toward the surface. 

 In general, there are lacking certain important features which 

 characterize the stems of both Gymnosperms and Dicotyledons, 



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