

SECT. V. THE LIGNEOUS LAYERS. 335 



ponent layers, so neither can you separate the two 

 sets of layers so as to exhibit each of them entire. 

 But as the divergent layers are soluble in fluids, in 

 which the concentric layers are not, the latter may 

 be exhibited pretty entire by means of the destruc- 

 tion of the former. Du Hamel macerated,, for a 

 long time, a piece of the trunk of an Oak-tree in 

 water, in which the divergent layers are soluble, 

 and found that the minuter divisions of the con- 

 centric layers consisted ultimately of an assemblage 

 of longitudinal fibres, so as to form a net-work 

 similar to that of the liber. The same thing may 

 be very distinctly seen in the stem of a full grown 

 Cabbage, that has been pulled up out of the soil, 

 and exposed for some considerable length of time 

 to the action of the atmosphere. The divergent 

 layers have been decomposed, and the concentric 

 layers are left insulated. But one of the best and 

 most beautiful of all examples of this kind is that 

 of the net-work exhibited in the layers of the large 

 roots of the Artichoke, which when exposed to the 

 weather till the divergent layers have been decom- 

 posed, present a multitude of skeletons of concentric Which 

 layers, forming a net-work of fibres as fine as a n 

 piece of lace. 



But this mode of analysis gives us no knowledge 

 of the structure of the divergent layers, because 

 they are decomposed in the process. We must 

 consequently have recourse to the aid of the mi- 

 croscope. And if a thin slice of one of them is 



