INTRODUCTION 



leathery^ fibrous, etc., explain themselves; but as the small 

 breathing holes which perforate it are not familiar objects, the 

 botanical term " Lenticels " must be employed. These lenticels 

 are perhaps most conspicuous upon the bark of the Silver Birch, 

 where they form the centres of long horizontal stripes, that 

 become longer as the tree increases in girth. Each species of 

 tree has its peculiar kind of lenticel, but as a rule they cannot be 

 readily found upon old trees where the bark is much fissured and 

 rugged : they must be sought for at the bottoms of the fissures 

 and upon the fragments of the original cuticle that often persists 

 upon the tops of the corky ridges. The bark at the base or butt 

 of the tree frequently differs from that which clothes the upper 

 portion. In the Birch again we have an example, for its bark, 

 though smooth and laminated like paper above, is usually rough, 

 fissured, and corky at the foot. If a section of the lower part 

 be taken, a mass of hard, rod-like, light- coloured bodies will be 

 seen imbedded. This may serve as a type of that which is to be 

 observed in other species, but in addition it must be noted whether 

 the bark is in two distinct layers (Raspberry- jam Tree) (Acacia 

 acuminata), and also whether the ends of the rays leave their 

 impression upon the inside of the bark (Beech, Oak) or, again, if 

 they are apparently continued some distance into the bark with 

 the woody part of the ray connected to the distal portion by a 

 " tongue-and-groove " (Oaks, Casuarinas). (Fig. 171.) 



If the bark be deciduous, as in the familiar Plane or Button-ball 

 tree of the London squares, it will naturally be but seldom found 

 upon a log that has travelled, nor will it be otherwise if it be not 

 firmly adherent. Some barks shrink more rapidly in a vertical 

 direction than the cylinder of wood within, and thus detach 

 themselves (Purpleheart, Copaifera), while others are firmly at- 

 tached to the wood and separated with difficulty (Boxwood). 



The outer surface of the naked log corresponds with the inner 

 surface of the bark, unless there is a considerable thickness of 

 bast between them. In any case the markings on this outer 

 surface may not only serve as a means of identification, but also 

 to show in what manner the grain or fibre of the tree runs, 

 whether spirally, as in the Lignum vitas, or sinuously, as in the 

 Australian Gum trees — both also important items from a technical 

 point of view. (See Figs. 163-167.) 



Beneath the bark of trees many insects find food and shelter 

 chiefly the larvas of beetles and moths. Some eat their way into 

 the solid wood to form cylindrical holes or galleries such as may 

 occasionally be seen even in Ebony and the Australian Ironbark. 

 Others confine themselves to galleries made in the newly-formed 

 wood immediately beneath the bark, and travel in a peripheral 

 direction only. As the wood removed by these parasites is still in 



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