Microscopical Essays. 677 



The interior pan of the tree may be further confidered as 

 divided into four principal concentric ftrata, the bark, the blea, 

 the wood, and the pith : to thefe Dr. Kill has added the corona. 

 Whatever part of a plant we examine, we find thefe and no 

 more. The root , it's afcending ftalk, and defccnding fibre, are 

 formed of one, and not three different fub fiances. Thus the 

 whole vegetable is reduced to one entire body. And what ap- 

 pears in the flower to be formed of altogether diflincl parts, will 

 be found to originate in thefe. 



The bark, which is the exterior covering of the tree, is divided 

 into two parts, a thin outer rind, and a much thicker inner one. 

 The exterior onefeems to be little more than a fine film of irregu- 

 lar mefbes, the inner one compofed of large blebs, leaving in fome 

 fubjecls large vacant fpaces, which form it's vafa propria. It is 

 made up of feveral flrata, laying one over the other. 



Next to this is the blea, which is of an uniform ftruclure. It 

 is an imperfect wood, waiting only for the hand of time to be 

 brought to perfection. The duration of the blea in this middle 

 flate depends on the internal powers and flrength of the tree, 

 being fo much fhorter as this is more vigorous. 



The wood, including the corona, comes next ; it differs in den- 

 fity and duration, both from the blea, the bark, and the wood. 

 It is made up of flrong fibres. The life of the vegetable feems to 

 refide in it • from it all the other parts are produced. It fhoots a 

 pith inwards, and a blea and a bark outwards. 



Every 



