SECT. II. COMPOSITE ORGANS. 225 



ginal layer separates into two parts, as Grew sup- 

 posed ; because the bark is augmented by a new 

 layer as well as the wood. 



Such is the final result of the experiments of Peculiar 

 Du Hamel, Hope, and Knight. And yet Mr. Knight, 

 Knight, who has done so much to elucidate the 

 subject, entertains at the same time some minor 

 opinions that are altogether incompatible with his 

 general theory. He is of opinion that the new 

 bark, as well as the leaf, possesses also the power of 

 preparing proper juice and of generating new wood; 

 because it was observed that a small quantity of 

 wood was generated even at the lower extremity of 

 an insulated portion of bark on which there was 

 neither bud nor leaf.* But is it not possible to 

 account for this small production from the quantity 

 of proper juice that might exist in the bark at the 

 time it was left in its insulated state ? He is also of 

 opinion that the wood or alburnum already formed 

 extends itself laterally without any radicles as he 

 calls them, descending from the leaves and shoots 

 above ; because trees of different species, when 

 grafted on one another, preserve their wood distinct 

 in quality immediately above and below the graft. 

 But if the wood extends itself laterally, why did it 

 not so extend itself above his insulated leaf, where 

 we are told it made no augmentation? And is it not 

 also possible that the proper juice may receive its 

 final degree of modification in the bark itself? 



* Phil. Trans. 1803. 

 VOL. II. 0, 





