CH. ir. 



COURSE OF THE SAP. 



67 



of tlie pith of the last year's shoot, stands witli as broad 



a basis as that of the seedhng. I think that this junction Diminu- 

 tion in the 



of tlie taper top of the pith of one year's shoot, with ^^^j^f^^J^® 

 the broad base of the pith of next year's shoot, is the pej^Ja^ce" 

 origin of the ideas that the pith of each shoot becomes 

 annually smaller than that of the shoot above it, by 

 the new annual pressure from without of the wood, 

 and that the pith eventually disappears. Both these 

 ideas are vulgar errors. Dr, Lindley believes (or did, 

 in 1849) of the pith, that 'its office of nourishing the 

 young parts being accomplished, it is of no farther im- 

 portance, and dies.' This may be so, certainly, but I 

 wonder what the Doctor's reasons are for thinking so ; 

 the same, perhaps, as for thinking that all heart-wood 

 is dead-wood. What other parts of the tree is the 

 Doctor prepared to dispense with ? That a tree will 

 live when the original central pith, and nearly all the 

 heart- wood, are dead and gone^ we know ; and so will 

 a man when one of his lungs is gone ; and the man and 

 the tree are equally benefited by the loss. 



The difference in size, between the top of the pith 

 of one year's shoot and the base of the next, may 

 also be seen in Plate I. And in regard to the dis- 

 appearance of the pith, even the layers of wood, which 

 may be counted on this board, give thirty years of age 

 to the lower pith, and twenty-nine to the upper one ; 

 but they are possibly much older, and perhaps half a 

 century of pressure from without has neither extermin- 

 ated them nor even reduced the lower end of the upper 



s 2 



