in pei’ennial trees a new alburnum, and con« 
sequently a new system of vessels, is annually 
produced, and the nutriment for the next year 
deposited in them ; so that the new buds, like the 
plume of the seed, are supplied with a reservoir of 
matter essential to their first development. 
The old alburnum gradually loses its vascular 
structure, and, being constantly pressed upon by 
the expansive force of the new fibres, becomes 
harder, denser, and at length becomes heart-wood ; 
and in a certain time obeys the common laws 
of dead matter, decays, decomposes, and is con- 
verted into aeriform and carbonic elements ; into 
those principles from which it was originally 
formed. 
The decay of the heart-wood seems to constitute 
the great limit to the age and size of trees. And 
in young branches from old trees, it is much more 
liable to decompose than in similar branches from 
seedlings. This is likewise the case with grafts. 
The graft is only nourished by the sap of the tree 
to w T hich it is transferred ; its properties are not 
changed by it : the leaves, blossoms, and fruits are 
of the same kind as if it had vegetated upon its 
parent stock. The only advantage to be gained 
in this way, is the affording to a graft from an old 
tree a more plentiful and healthy food than it could 
have procured in its natural state : it is rendered 
for a time more vigorous, and produces fairer blos- 
soms and richer fruits. But it partakes not merely 
of the obvious properties, but likewise of the infirmi- 
ties and disposition to old age and decay, of the tree 
whence it sprung. 
