665 



Microscopical Essays. 



opened by the feafon of the year, either before the nrft leaves of 

 fpring, or in the midfummer {hooting time ; though a final 1 quan- 

 tity of mo i Pane will keep them open at that time, yet no quai> 

 tity v/ould be funicient at an improper feafon.* 



The blea is a zone more or lefs perfect, which lies under the 

 bark, and covers or furrounds the wood, and is principally diftin- 

 guifhed from it by being lefs denfe. In fome fpeeies the difference 

 between the blea and the wood is very remarkable, in others it is 

 lefs fo. 



The ancient botanifts, (truck with the difference they obferved^ 

 between the wood and the blea, compared this fubftance to the 

 fat in animals. Malphigi, Grew, and Duhamei conhder it as 

 the wood not yet arrived to a ftate of perfection. It is organized 

 in a manner fimilar to the wood, and poffeffing the fame veffels, 

 difpofed nearly in the fame manner. The juice veffels of this- 

 part may be feparated from it by maceration ; Dr. Hill fays, that 

 in this ftate they appear perfect cylinders, . with thick white coats ? 

 the furface perfectly uniform. 



Of the Wood. 



When the bark and the blea is taken away, we come to the 

 wood, which is a fol id fubftance, on which the ftrength of the 

 tree depends, and which has been confidered by naturalifts as 

 being to the tree what bones are to the animal. The wood, in a 

 general view, may be confidered as formed of ftrata, which are 

 inclofed one within the other ; thefe ftrata confift of lignous 



fibres 



* Hill's Conftru&ion of Timber. 



