36 



is due to Darwin) ; that the fibres are the 

 roots of the buds, which, at the bursting 

 of the buds, run between the last year's 

 bark and wood to the ends of the roots. 

 Those who can assent to this theory may 

 flatter themselves that they know some- 

 thing of the growth of trees in diameter ; 

 those who cannot believe it must confess 

 their ignorance on the subject. To say 

 that the new layer of wood is formed 

 from the viscid substance to which Grew 

 gave the name of cambium does not remove 

 the difficulty. \'VTience is the cambium it- 

 self formed? How and where elaborated ; 

 how organised ? 



Dutrochet and Link bring us back to 

 Hales' s doctrine of the all-importance of 

 the pith. Indeed Dutrochet would estab- 

 lish the omnipresence of the pith. He tells 

 us that each division between the annual 

 layers of wood is a pith for the layer 

 outside it ; and that, in addition to the 

 original medullary rays, which run from 



