2 OF WOOD IN GENERAL. 



employment of the material, but by the vital requirements of the 

 tree when growing. 



Our present concern is with wood as a material in the arts, and 

 not with any merely botanical interest it may have, or with its 

 cultivation as a crop by the forester. In dealing with the means 

 of recognizing different kinds of wood we shall, therefore, not 

 depend in any way upon characters derived from bark, leaves, 

 flowers, or fruit the characters, that is, of standing, or of un- 

 converted timber; but only on those of the wood itself as it 

 appears in the timber market. At the same time, if we are to be 

 able to identify woods and determine their suitability for various 

 economic applications, it is absolutely essential that we should 

 know something of their origin, structure, development, and use 

 to the plants that produced them. 



Wood does not occur in any plants of a lower grade than ferns ; 

 and in the higher plants in which it does occur it is chiefly, but 

 not exclusively in the stem. In the shell of the cocoa-nut or the 

 stone of a peach it probably serves the purpose of checking pre- 

 mature germination of the enclosed seed by excluding damp. In 

 stems, however, the main physiological function of wood is the 

 mechanical one of giving strength to resist the increasing weight 

 of the structure as it grows erect and branches. Submerged 

 aquatic plants, buoyed up, as they are, by the water, do not form 

 wood in their stems, nor, as a rule, do annuals, nor, at first, the 

 succulent, flexible shoots of longer-lived plants. In ferns, even 

 when growing into lofty trees, and in allied plants, the wood, 

 though dense, consists largely of scattered longitudinal strands 

 and often of cells of no great vertical length. Though there are 

 also generally woody layers just below the surface of the stem, 

 giving it considerable strength as a whole, this structure renders 

 tree-ferns useless as timber. 



For all practical purposes, therefore, wood is produced only by 

 the highest sub-kingdom of the plant world, the seed-bearing or 

 flowering plants, the Spermatophyta or Phanerogdmia of botanists. 

 This great group of plants is sub-divided, mainly by characters 

 derived from parts other than their stems, into two divisions, the 



