Microscopical Essays. 66j 



fibres or lymphatic veffels, the cellular web or tiflue, vafa pro- 

 pria, and what have been called the air veffels. It is more difficult 

 to invert igate the conflruclion of the wood than that of the other 

 parts, becaufe the texture is in general much harder, and there- 

 fore not fo eafily feparated, requiring very long macerations, and 

 many fubjecls, before one may be found fit for examination. 



If we examine a tranfverfe fection of almoft any kind of wood, 

 we (hall perceive thefe flrata very clearly and fenfibly diftinguifti- 

 ed from one another. It has been generally fuppofed, that each 

 of thefe is the producl of one year's growth; though if we cut the 

 fame wood obliquely, we (hall perceive that each of thefe flrata 

 is compounded of fmaller ones, which are, therefore, not fo eafy 

 to difcover as the larger. By macerating rotten pieces of trees, 

 the wood may be divided into an immenfe number of leaves, or 

 flrata, thinner than the fined paper. 



If the foregoing flrata are examined in their detached flate by 

 the microfcope, we {hall find them to be compofed of longitu- 

 dinal fibres ; fome pieces of rotten wood, after maceration, will 

 divide of themfelves into very fine longitudinal fibres ; the exifl- 

 ence of thefe is further proved by the facility with which wood 

 may be fplk in the direction of thefe fibres. From hence we 

 may collect, that the lignous flrata are formed of fmall fibres or 

 Veffels, collected together in fafcicles, like the bark: in fome 

 trees they are parallel to each other, in others they are difpofed 

 more obliquely, c rolling and forming an irregular kind of net- 

 work. There is great probability that this reticular difpofition 

 exifls in all trees, though it may be difficult to difcover it in many 



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