184 VEGETABLE ORGANOGRAPHY. 



interior. Duhamel, who perceived these reasons for 

 doubting, has not ventured to draw any direct conclu- 

 sions. Mirbel, who repeated his experiment, concludedj 

 first, that the liber changes into alburnum ; he has since 

 only said that the liber divides itself between the wood 

 and the bark. Knight, Mustel, Du Petit-Thouars, 

 Dutrochet, &c. have, on the contrary, maintained that 

 the liber does not change into alburnum ; and this 

 opinion has always appeared to me most conformable 

 to the generality of facts. Kieser arrives at the same 

 conclusion, in consideration of the difference of the 

 tissues of the liber and alburnum. 



The third opinion, which tends to establish that the 

 alburnum forms the woody layers, and that the liber 

 produces the cortical ones, has been maintained, first 

 by Mustel, and since by Dutrochet. The former is 

 contented with denouncing the opinion, that the ascend- 

 ing sap of the woody body forms a kind of liber, which 

 is converted into alburnum; and that the sap descending 

 by the bark forms a kind of cortical liber, which is con- 

 verted into true bark. It is founded partly upon an inac- 

 curate observation ; viz. that the woody layers are formed 

 in the interior of the medullary canal ; whence it is con- 

 cluded that they maybe as well formed upon the outside 

 of the woody body. The inaccuracy of the opinion of 

 Mustel, as to the function of the two saps, appears to me to 

 be sufficiently demonstrated by an often repeated observa- 

 tion, that the woody layers which are formed are thicker 

 in proportion as the access of the descending sap is more 

 easy. Dutrochet has given more precision in his re- 

 searches in this respect ; he has made them chiefly upon 

 herbaceous Dicotyledons, seeing that the compact and 

 close tissue of woody plants renders them, according to 

 him, more difficult to be observed. He was the first to 

 remark, that under the name of the increase of trunks 



