170 VEGETABLE ORGANOGRAPHY. 



these trees, which Adanson, by calculation, supposes 

 to have amounted to several thousand years. 



When traces of any ancient inscription are found upon 

 old barks, they may serve as indications for looking for 

 this inscription in the corresponding part of the woody 

 body ; and if it had originally penetrated the alburnum, 

 concealed traces will be found under the woody layers : 

 in this case, an exact verification both of the age of 

 the inscription, and of that of the tree, is obtained. If 

 Adanson had been able to make this research upon the 

 Baobabs, we should have had a more certain document 

 of the real age of these veterans of the organized world. 

 The fact, as it has been transmitted to us, already suf- 

 ficiently tends to prove the extraordinary age to which 

 trees may attain ; for, although he may have erred with 

 regard to centuries, still this longevity very much sur- 

 passes the duration which one would suppose possible 

 for any organized being. 



Independently of the circumstances which result from 

 their position and their mode of increase, the cortical 

 layers differ also from the woody layers in several 

 respects. In general they are not so thick ; they have 

 few or no tracheae ; they contain more receptacles of 

 proper juices ; in equal weights they contain more car- 

 bon ; they are much less endowed with the hygroscopic 

 property : lastly, when a plant or a branch is plunged into 

 water, the sap does not rise into the bark. 



The cortical fibres, in several plants, are remarkable 

 for their flexibility and firmness ; as is seen in those of 

 the Hemp, Flax, several species of Nettle (Urtica), 

 several of the Malvaceae, &c. All the fibres capable of 

 being made into cordage, and of being spun, &c., ob- 

 tained from Exogens, are the product of their bark. 



