32 OF WOOD IN GENERAL 



concentric zones, often stretching as wavy, pale, bar-like markings 

 from one primary pith-ray to another, and sometimes running into 

 one another. These " false rings," as they have been termed, 

 which are seen in the wood of Figs, She-oaks [Casuarina), Poon 

 (Calophyllum), etc., will be found on microscopic examination to 

 be mainly produced by zones of wood-parenchyma. 



The grouping of the vessels also affords some useful distinctive 

 characters. Thus in Box and in Quince they usually occur singly ; 

 in Hazel and Holly in groups of from 5 to 12 ; in Hornbeam in long 

 sinuous radial lines between the pith-rays ; in Elms in concentric 



Fig. 28.— Transverse section of Buckthorn {Rhdmnus cathdrticus), showing flame-like 

 groups of vessels. 



bands like false rings ; and in Oaks, Chestnut and Buckthorn, from 

 20 to 50 together, in flame-hke groups (Fig. 28). 



The elements of the wood are generally parallel in direction 

 to the axis of the stem or limb in which they occur — i.e. the wood 

 is straight-grained ; but they may be spirally twisted round the 

 stem, or oblique, in which latter case if successive layers lie in 

 opposite directions the wood is cross-grained. A slightly wavy 

 longitudinal course in the elements of the wood produces the 

 condition known as curly grain, frequent in Maple ; whilst slight 

 projections or depressions repeated on the outer surface of suc- 

 cessive annual layers produce the bird's-eye and landscape varieties 

 in the same wood. The presence of undeveloped buds or knots, 



