ON THE DIFFERENT SORTS OF WOOB. 



^67 



wood became old ; but it only leaves the intermediate parts, 

 which constantly contract. The sap vessels are rather en- 

 larged than lessened by age; and grow vastly firmer by the 

 strong support they thus gain by reduction. 



I shall now turn to the wood of annual or herbaceous Trying crf- 

 plants :- it is formed of two sorts, those which like the shrub J^u^n^^^/" 

 have only a narrow piece of ligneous matter ; and those the 

 wood of which is formed in compartments, something like 

 the manner of the leaf stalks, that is, round vessels of wood 

 surrounded by albumen, which altogether appear infinitely 

 larger than the common vessels so denominated, the spiral 

 wire being enclosed within the wood. These vessels are set 

 like spots in the circular pith; the number of sap vessels 

 increases, if the plants last a long season, as well as the 

 rows in the herbaceous vegetables, if fine weather prolong; 

 their existence : this 1 have before hinted at, in a former 

 letter, Vol. XXVIII, p. 249. It would seem that this al- 

 bumen, as well as that which surrounds the ligneous vessels 

 in the leaf, never became wood ; for let the vegetables be 

 ever so old, it still retains the clear and unformed appearance 

 it has at the first moment ; and let it be where it will, it is 

 always to be known. It is this we call nourishing vessels in 

 the leaf. 1 think it should be called by the name of clear 

 albumen, to distinguish it from that which afterward be- 

 comes wood. I have examined both; and, as far as the 

 eye can judge, they appear perfectly the same; but in 

 taste the clear albumen, which is that found in the seed, 

 the leaf stalk, and herbaceous plants, is bitter, which the 

 other is not, the other albumen is the new row of wood in 

 trees and the foundation of the seed, with the first formation 

 of the embryo. In all these the sap vessels afterward shoot. 

 When I tried both by decomposition the residuum was the 

 same; indeed the matter 1 can get for trial is so little, it is 

 hardly a fair chemical process, 



I should have continued to give an account of the ideas of 

 Aubert du Thouars, could I have thoroughly understood the 

 rest of his opinions; but he is not so intelligible as de Mir- 

 bel ; and (if I may be allowed to say so) has rather too much 

 given way to system and imagination. I should suppose it is 

 necessary t6 pass from step to step in this study, perfectly 



distinguishing 



