Theory of the Origin of Wood. 371 



these observers suppose that woody fibre is not formed but 

 by the aid of buds or leaves. Here then occurs the question 

 as to what is woody fibre. And can any essential difference 

 be pointed out between it and the cellular tissue in which it 

 is imbedded ? The most prominent features of woody tissue 

 are its length, and the hardened secretions which are deposited 

 in its interior. But these are not positive differences, as cel- 

 lular tissue, as it is called, is frequently found elongated as in 

 the tissue called " pitted" or Bothrenchyma ; whilst on the 

 other hand we frequently find it in a state as hard as that of 

 the most hardened woody tissue, as in the endocarp of many 

 fruits. If then the term wood in these passages is intended 

 to apply to all hardened lengthened tissue, we ought to be 

 able to trace its origin to leaves or buds wherever it is found. 

 But in many instances we have lengthened and hardened tis- 

 sue, or both combined, in cry ptogamic plants, which develope 

 no buds or leaves, as in some species of fungi belonging to the 

 genera Thelephora, Boletus, &c. 



There are also many parts of phanerogamous plants which 

 possess hardened and lengthened tissue, which do not appear 

 to come under the descending: influence of the fibres from 

 leaves or buds, such as the endocarps of amygdalaceous fruits, 

 and the pericarps of a great variety of other fruits. The pe- 

 duncles or flowerstalks in many plants possess woody tissue, 

 but have no leaves, as also the stems of many endogenous 

 plants which have no regular leaves. 



Among the stems of exogens and endogens we shall find 

 that there are many instances in which wood is formed with- 

 out leaves. I have examined the stems of leafless monotropas, 

 and find they possess woody tissue. In the stems also of leaf- 

 less Cactacece woody tissue is deposited in abundance. If we 

 examine also trees that have been wounded, we shall find that 

 the lower lips of the wound have been filled up with woody 

 tissue, and in such a manner as not to be explained upon the 

 supposition that the wood at this point has been formed by 

 the descent of fibres that had been formed and sent down 

 from the leaves. 



Another point to which I would wish to direct attention is 

 the formation of woody fibres in tissue formed after trees have 



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