BOTANY FOR YOUNG PKOPLE. 149 



E. In an endogenous manner. The layers 

 are added from the inside, and push the former 

 matter out, so that it cracks and breaks in every 

 direction, causing that roughened appe:u\u:ce 

 we see in the Oak and Elm. 



The bark of some trees is so hard and inflexi- 

 ble that it will not yield, but splits and breaks 

 off every season ; such is the Plane tree. On 

 the other extreme, is the Cork tree, whose bark 

 does not harden for a number of years, and 

 being stripped off while soft answers a variety 

 of purposes in the arts. 



If you take a gimblet and bore through the 

 bark till you just reach the alburnum, as the 

 successive coats of bark are deposited internally, 

 and push the others out, the gimblet will, after 

 a while, drop to the ground. In this way in- 

 scriptions on the bark of trees are effaced by the 

 distension and consequent cracking. 



L. But if the gimblet enters the alburnum 

 some distance, it will not drop off. but be held 

 tighter every year. 



E. Even an inscription made deep enough to 

 penetrate the alburnum will remain uninjured. 

 A story is told of the great traveller Adamson 

 finding a t re r. sure in this way. He relates that 



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