GROWTH. 125 



taken from a tree with white wood, and placed upon a 

 stock whose wood is red, in the course of proper time a 

 new woody layer arises, which, so far as the bark of the 

 scion goes, exhibits the colour of the scion's wood, but 

 below this shows the colour of the stock ; now were the 

 fibres from which the new wood is formed the roots 

 from the buds above, the wood ought to have the same 

 colour all the way down from the scion from whose 

 buds it would be produced ; but it is not so coloured, 

 and therefore it could not have been generated by the 

 buds above. 



189. Dr. Lindley, however, discussing this subject, 

 says, in regard to similar facts: "They are true; but 

 do not warrant the conclusion which have been drawn 

 from them. One most important point is overlooked 

 by those who employ such arguments, namely, that in 

 all plants there are two distinct simultaneous systems of 

 growth, the cellular and the fibro- vascular, of which the 

 former is horizontal, and the latter vertical. The cellu- 

 lar gives origin to the pith, the medullary rays, etc. 

 The character of wood is chiefly owing to the colour, 

 quantity, size, and distortions of the medullary rays 



which belong to the horizontal system," " as the 



medullary rays develope in a horizontal direction only, 

 when two trees in which they are different, are grafted 

 or budded together, the wood of the stock will continue 

 to preserve its own peculiarity of grain, notwithstanding 

 its being formed by the woody matter sent down by the 

 scion ; for it is the horizontal development that gives 

 its character to the ' grain of wood,' and not the per- 

 pendicular pleurenchyma encased in it." Notwithstand- 

 ing this a dissentient from the views of Du Petit Thouars 

 may say that the colouring matter in the Diospyros 

 ebenum Retz, is to be found within the fibre of the 

 wood itself, and though it is true, only in the short 

 pleurenchyma its origin is sufficiently shown, and that 

 this is also the case with Coesalpinia brasiliensis, Coe- 

 salpinia tapan, and others ; and " in Tiger- wood the 

 long cells of the wood have their membrane somewhat 

 M 3 



