CH. IV. 



MISCELLANEOUS. 



109 



tinue to deposit new growth on it from above. This 

 tree is still ahve (1844), having lived, possibly, nearly 

 forty years in this state. 



I imagine that the reason that this tree has con- 

 tinued to live is, that each year it has shot out new 

 branches from below the scar. These branches have 

 each year been eaten off by cattle ; but they have 

 elaborated and returned sufficient sap to nourish the root 

 and to keep it alive. I imagine that, if these branches 

 had been allowed to grow, they would have taken so 

 much sap that it would have ceased to be forced up 

 the old stem, and that the old stem would have died. 

 So that, but for the annual outburst of shoots below 

 the scar, the roots of the tree would die ; and but for 

 the annual browsing of these shoots, the head of the 

 tree would die. Yet on this precarious tenure the 

 tree has for so long held its existence. But the 

 existence of this tree and of ringed branches proves 

 to ocular demonstration that the sap goes up the heart- 

 wood, since on the scar and on the rings no new wood 

 or alburnum is deposited. It is true that the number 

 of rings of what is called sap-wood or alburnum differ 

 in different trees, and even parts of the rings of a tree 

 may ripen sooner into heart- wood than other parts of the 

 same rings, so that on the same transverse section of a 

 tree there shall be more rings of sap-wood on one side 

 than on the other. This may be observed in oaks ; 

 but on the scar of this tree no alburnum or sap-wood 

 has been deposited for possibly nearly half a century. 



