4 OF WOOD IN GENERAL. 



which do so have generally unbranched stems which do not as 

 a rule increase in diameter after the very earliest stages of their 

 growth, the wood in them being confined to isolated strands 

 crowded together towards their outer surfaces. Though such 

 stems may occasionally, like those of tree-ferns, be utilized "in 

 the round," and veneers, cut from the outer part of the stem of 

 the Cocoa-nut Palm (Cdcos nudfera), and known, from the appear- 

 ance of the dark-coloured woody strands in the lighter ground- 

 tissue, as "Porcupine- wood," are used for inlaying, Monocotyle- 

 dons may well be ignored as economic sources of wood. 



Dicotyledons, so named from having two seed-leaves to the 

 embryo, comprise an immense and varied assemblage of plants, 



FIG. 1. Transverse section of an Oak, 25 years old. After Le Maout and 

 Decaisne, from The Elements of Botany, by permission of Mr. Francis Darwin 

 and the Syndicate of the Cambridge University Press. 



a very large proportion of which are merely herbaceous, never 

 forming wood. In those perennial members of the Class, how- 

 ever, which acquire the dimensions of trees or shrubs, the stem 

 generally branches freely, has a separable "bark," and increases 

 in girth with age ; the wood, though, as we shall see, it differs 

 in several important but not very obvious characters, agreeing 

 with that of conifers in being arranged in rings produced in 

 successive seasons (Fig. 1). These rings, as they appear in a 

 cross-section of a tree, or conically tapering sheaths surrounding 

 the tree, as they in fact are, form on the outside of the wood of 

 previous seasons and beneath the bark ; and this type of stem, 

 characteristic of gymnosperms and dicotyledons, is in consequence 

 correctly termed exogenous, from the Greek ex, outside of, and 



