Microscopical Essays. 



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one, which is frefher, "and adheres more firmly to the bark. 

 Perennial plants are fupplied in this manner with a new fldn every 

 year ; the outer one always falls off in the autumn and winter, 

 and a new one is formed from the bark in the fucceeding fpring. 



Of the Vessels which are contained between the 

 Rind and the Bark. 



Thefe are called by Duhamel the cellular coat, (eriveloppe 

 cellulaire) by Hill the exterior veffels, and the vafa propria 

 exteriora. 



It has been already obferved, that in trees the juice veflels, or 

 vafa propria, do not form thofe conftituent parts of the wood of 

 which the timber confifls, but that it is from the nature of thefe 

 recipient veflels that it derives it's virtues, qualities, and fpecific 

 properties.* A tree may grow, live, and give fliade without 

 them ; but on thofe it's peculiar character and decided virtues 

 depend ; thefe are greateft where the vafa propria are larger! or 

 molt numerous, and where we do not find thefe, we fcarce find 

 any thing that will affect the tafle or the fmell. There are differen t 

 ranges of thefe veffels between the feveral parts, each of which 

 has it's allotted place, it's peculiar form, it's different ftru&ure, 

 and it's feparate ufe. Many trees have them in all their parts, 

 others only in fome of them, while others do not exhibit any. 



Gn taking off the rind, we find a fubftance of a deep green 

 eolour, fucculent and herbaceous, formed of a prodigious number' 



4 L 2 of 



* Hull's Gonflrudion of Timber, p. 73. 



