SECT. II. COMPOSITE ORGANS. 223 



of elucidation on one of the most obscure and intri- 

 cate processes of the vegetable economy, in having 

 shown that the sap is elaborated, so to render it fit As elab- 

 for the formation of new parts, in the leaf only. If the 6 leaf, 

 a leaf or branch of the vine is grafted even on the 

 fruit-stalk or tendril, the graft will still succeed ;* 

 but if the upper part of a branch is stripped of its 

 leaves the bark will wither as far it is stripped ; and 

 if a portion of bark furnished with a leaf is insulated 

 by means of detaching a ring of bark above and below 

 it, the wood of the insulated portion that is above 

 the leaf is not augmented :-f~ this shows evidently 

 that the leaf gives the elaboration necessary to the 

 formation of new parts, and that without the agency 

 of the leaf no new part is generated. 



There seems indeed to be an exception to this Or even 

 law in one of Mr. Knight's own experiments, in 

 which he found that when the fruit-stalk was grafted 

 on the leaf-stalk, the graft succeeded also ; and in 

 which case the wood was deposited on the external 

 sides of his central vessels, having oozed, no doubt, 

 from the external tubes by which the proper juice 

 descends. Now this seems to prove that the parts 

 of the flower are capable of generating wood as well 

 as the leaf: but it should be recollected that flowers 

 in general are furnished with a calyx, which is cer- 

 tainly very nearly allied to the leaf, and that some 

 parts of the flower are even convertible into leaves ; 

 * Phil. Trans. 1803. f Ibid, 1801. 



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