202 BOTANY. 



In the trunk of the tree there is a series of con- 

 centric layers, the number of which denotes the age 

 of the tree. They are the accumulated remains of 

 by-gone generations, in which vegetation and life are 

 entirely extinct. 



The Liber (or Inner Bark). 



When vegetation revives in the woody plant on 

 the return of spring, it is because a new liber has re- 

 placed in the cortex, or rind, the liber of the preced- 

 ing year, which has hardened and become wood. All 

 the great and ancient trees vegetate solely by their 

 herbaceous layers of liber, annually produced at the 

 inner surface of the bark. 



Parenchyma. 



Immediately under the epidermis, is a spungy, 

 porous, cellular substance, named the Parenchyma. 



The Age of Trees. 



In consequence of the slow decay of the heart- 

 wood of the oak and chestnut, those trees, under 

 favourable circumstances, attain an age which cannot 

 be much short of 1000 years. The beech, the ash, 

 and the sycamore, most probably never live half so 

 long. The duration of the apple-tree is not probably 

 much more than 200 years; but the pear-tree, ac- 

 cording to Mr. Knight, lives through double that 

 period. Most of our best apples are supposed to 

 have been introduced into Britain by a fruiterer of 

 Henry VIII., so that they are now in a state of ex- 

 treme old age.* 



* Bishop Watson says: " Planters of trees ought to encourage 

 themselves by considering all future time as present; indeed, 

 such consideration would be a useful principle to all men in their 

 conduct of life, as it respects both this world and the next." 



