2 OF WOOD IN GENERAL 



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

 able to identify woods and determine their suitabihty 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. 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-Hved 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 aU practical purposes, therefore, wood is produced only by 

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

 flowering plants, the 8f&rmatofhi^ta 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 

 Gymnosfirmce, or plants the seeds of which are naked, i.e. not 

 enclosed in a fruit, and the AngiospermcB, or fruit-bearing plants. 

 The Gymnosperms are all perennial trees and shrubs ; but of 

 three " Natural Orders " into which they are divided, two, the 

 Cyoaddcem and Onetdcece, belong almost exclusively to the Southern 

 Hemisphere and are valueless as timber. The third Natural 

 Order is the Coniferce, so named from the general arrangement of 

 its seeds on a series of overlapping scales arranged in a cone, but 

 having also other general characters, one of the most conspicuous 

 of which is the production of numerous narrow, ridd, undivided 

 leaves, whence they get the famihar name of needle-leaved tree,. 

 The members of this Order, which includes the Pines, Firs, 

 Larches, Cedars, etc., have much-branched stems, and wood 

 which, though in many points, such as its arrangement in annual 

 rings of growth, it resembles that of some other, more highly- 

 organized plants, has, as we shall see, many pecuHarities. It is, 

 in general, of rapid growth, soft and of even texture, and very 

 commonly abounds in resinous substances. They are, therefore, 

 often spoken of as " soft woods " or as " resirious woods/' and being, 

 from these characteristics, both easily worked and of considerable 



