SECT. V. 



THE LIGNEOUS LAYERS. 33 J 



an Oak, found only fourteen on the other. But 

 the fourteen exceeded the twenty in thickness by 

 one fourth part.* They are also generally thicker 

 in the root than in the stem and branches., as has 

 been already remarked with regard to the layers of 

 the bark. 



But the layers thus discoverable on the hori- And al- 



* 1 1 r i wa y s un ~ 



zontal section of the trunk are not all 01 an equal e qual in 

 consistency throughout, there being an evident 

 diminution in their degree of solidity from the 

 centre where they are hardest, to the circumference 

 where they are softest. The outermost layer, which Forming 

 is the softest of all, is denominated the Alburnum, alburnum, 

 perhaps from its being of a brighter white than any 

 of the other layers, either of wood or bark, from 

 which character, as well as from its softer texture, 

 it is also easily distinguished, though in the case of And in- 

 some plants, as in that of the Poplar and Lime-tree, perfect 

 this peculiarity of character is not very apparent. wood - 



From the peculiarity of external character how- 

 ever, which it possesses in general, it was at one 

 time thought to be a substance essentially different 

 from that of the layers which it invests. The an- 

 cients, whose phytological opinions were often very 

 whimsical, supposed it to be something analogous 

 to the fat of animals, and intended perhaps to 

 serve as a sort of nutriment to the plant in winter. 

 But it is now known to be merely wood in a less con- 

 densed state,, being yet lighter and softer than the 

 * Phy?. dcs Arbrcs, liv. i. chap. iii. 



