168 VEGETABLE ORGANOGRAPHY. 



perfectly entire, and are not distended in any direction ; 

 whilst the cortical layers, being placed upon each other 

 in a contrary direction, must gradually undergo con- 

 siderable distension. In fact, the first layers of bark 

 '.vhich are developed when the stem is very small, are 

 pushed to the outside, and distended, either by the for- 

 mation of new layers, larger than they are, and situated 

 on the inside ; or by the progressive increase of the 

 woody body. Likewise, although the number of cor- 

 tical layers which are formed in the trunk since its 

 development may be equal to that of the woody layers, 

 they are of a very different kind : those of the bark, dis- 

 tended by_the increase of the trunk during the first year, 

 always present fibres more or less bent, and this dispo- 

 sition goes on augmenting as they advance in age ; whilst, 

 on the contrary, the fibres of wood remain usually recti- 

 linear. 



The woody layers remain in the state of alburnum, 

 until, by the natural deposition of nutritive particles, 

 they have acquired the hardness which they ought to 

 have ; the cortical layers, distended, and half destroyed, 

 before this period, very soon lose their freshness, and 

 never acquire the same degree of solidity. The former 

 constantly preserve their thickness ; the latter have a 

 tendency to become thin by the distension and separa- 

 tion of their fibres. The former, protected from the 

 influence of the atmosphere, preserve all the appearance 

 of life ; the latter, exposed to the action of the air and 

 light, tend to dry up, to crack, and to take deeper colours : 

 thus, the cortical layers, by the effect of their position, 

 are first distended in such a manner, as to enclose the 

 trunk, as it were, in a case ; afterwards they split longi- 

 tudinally ; then they crack more or less ; and whilst 

 these phenomena are taking place, they become more or 

 less black, or brown, externally. 



