Microscopical Essays. 



66 3 



branches, or fuffering any change in their fize and fhape. Hence 

 the bark may be tore or divided lengthways, with greater eafe 

 than in an horizontal direction ; when macerated, they are capa- 

 ble of a very great degree of fubdivifion. 



The filaments of a cortical veffel are to be looked on (agreea- 

 ble to what we have already obferved) as fo many little bundles 

 placed near together, and at firft growing parallel to each other ;. 

 but foon quitting this direction, the filaments of one fafcicle part- 

 ing from that to which they originally belonged, and inclining 

 more or lefs obliquely towards another, fometimes uniting with 

 it, at others bending backwards, and uniting again with that from 

 whizh it proceeded, or with Tome one that it meets with. In this 

 manner new fafcicles are often formed, while other parcels are 

 increafed or diminifhed by the additions of new filaments; by 

 this means, a kind of irregular net is formed, and the fibres pro- 

 ceed in a ferpentine line from the top to the bottom of. the., tree. . 



The thicknefs of the bark is entirely formed of ftrata of thefe 

 longitudinal fibres, which lie one over the other; each of thefe 

 ftrata is fimilar to the exterior one, only the mefhes are fmaller, 

 and the fibres finer, in proportion as they are more interior, in- 

 fomuch that at laft the- melhes are al mo ft annihilated, and the 

 fibres feem to lie quite, parallel to each other. 



- There arefome trees, however, v/here the mefiies are not vifible, 

 and , in which the. fibres lie quite in a. trail direSion. There are 

 many other circumftances in which they vary in different trees ; 

 im fome the mefiies of each .ftratum correfpond with each other, , 

 £ diminifiV - 



