

SECT. II. COMPOSITE ORGANS. 235 



process of induration ; unless you suppose that the 

 matter carried off from the alburnum in the spring, 

 by means of the ascending sap, is again deposited 

 in it in the course of the summer. And this is 

 indeed what Mr. Knight supposes ; for he thinks 

 that the proper juice in descending from the leaf is 

 expended not only in forming a new epidermis, 

 where that is wanted, and a new layer of liber and 

 of alburnum, but partly also in entering the pores 

 of the former alburnum and mingling again with 

 the ascending sap. But if this second accession 

 of proper juice were even allowed, its effect could 

 be but very trifling. For if it mingles again with 

 the ascending sap, it must also be again for the 

 most part carried off, and can consequently be of 

 no great advantage to the induration of the wood. 

 And if it should even leave behind it a considerable 

 deposit, now, in the second year, still you have 

 to account for its further induration in the third 

 and fourth and subsequent years, when it will 

 hardly be contended that the descending proper 

 juice enters it. It cannot, therefore, be admitted 

 upon Mr. Knight's principles that the alburnum is 

 converted into wood by means of any matter de- 

 posited in it during the summer ; because the 

 matter thus deposited is again carried off in the 

 succeeding spring; and is not proved, but con- 

 jectured, to be again restored in the summer fol- 

 lowing : on which very slender foundation Mr. 

 Knight has, however, thought proper to erect the 



