334 COMPOSITE ORGANS. CHAP. II. 



layers cannot always be so traced. Daubenton says 

 he could not trace any of them quite to the pith, 

 but that is by no means the case in all species of 

 wood. 



Such then is the general aspect of the ligneous 

 layers whether concentric or divergent, as discovera- 

 ble in the transverse or horizontal section of the stem 

 or branch. But it is necessary to pursue the in- 

 vestigation still farther, and to endeavour to ascer- 

 tain the component parts of the layers themselves., 

 till they are at last reduced to their ultimate and 

 elementary organs. 



SUBSECTION III. , 



Concen- Structure of the Layers. If any one of the 

 concentric layers, as they present themselves at first 

 sight on a horizontal section of the stem, is taken 

 and inspected minutely, but particularly with the 

 help of a good glass, it will be found to consist of 

 several smaller and component layers, which are 

 themselves composed of layers smaller still, till at 

 ^ast they are incapable of farther division. In the 

 Alburnum the aggregate mass of layers is very 

 often separable merely with the hand assisted by a 

 fine instrument, but in the matured wood it is se- 

 parable only by maceration or decay. But the 

 divergent layers do not seern capable of division 

 into finer layers, whether by the knife or macera- 

 tion. And as you cannot divide them into coin- 



