SECT. V. THE LIGNEOUS LAYERS. 333 



verse plates being of a deeper shade of colour than 

 the rest of the wood, as may often be observed 

 even in the flooring or wainscoting of a room, of 

 which the materials are oak. 



The divergent layers were at one time, and with Impro- 



A 



some botanists are still, denominated the Medullary 

 Rays, upon the supposition of their originating 

 in the pith. This opinion was entertained by 

 Du Hamel, and supported by the following fact : 

 Having taken the trunk of a Lime-tree of about 

 four or five inches in diameter, about the middle 

 of which there was a bud, and cut it asunder ob- 

 liquely in the direction of the bud, and having 

 examined the section with great care, he thought 

 he could trace a ray of a whiter shade than the rest 

 of the wood, extending from the pith to the bud. 

 The conclusion therefore was, that the bud is 

 formed from the pith, and that the ray extending 

 from the one to the other is with propriety deno- 

 minated a medullary ray.* But if it is only recol- 

 lected that buds are formed on the surface, and rays 

 in the interior of the trunk, long after the pith 

 has disappeared in the centre, the impropriety of 

 the appellation of the medullary rays will be ren- 

 dered evident, as well as the necessity of looking 

 out for a different origin both to the bud and ray. 

 The thicker and more conspicuous of the divergent 

 layers may indeed be traced from the circumference 

 to the centre ; but the thinner and intermediate 

 * Phys. des Arbres, liv, i. chap. iii. 



