350 Mr. Knight's Experiments on 
more durable. Some portion of this increased durability may, 
perhaps, be attributable to the superior solidity of the coloured 
wood ; but, a little attention to the common kinds of English 
timber, (omitting the resinous tribe,) will convince us that these 
qualities, though frequently found together, have very little con- 
nection with each other. If a number of oaks of the same age 
be examined, it will be found that, in some individuals, the 
alburnum consists of a greater number of annual layers than in 
others, and that the coloured wood will have approached nearer 
the bark on one side than on the other, in the same tree ; the 
termination also of the coloured wood, and the commencement 
of the alburnum, are often found in the middle of an annual 
layer of wood ; and each substance, at the points of contact, pos- 
sesses all its characteristic properties. The alburnum, I think, 
evidently extends itself laterally, without any radicles descend- 
ing from the leaves or buds above. I have often procured an 
union, by grafting, between trees of different kinds, and have 
sometimes found mere varieties of the same species of tree, 
whose wood was sufficiently distinguishable, in every stage of 
future growth, to allow me readily to trace their line of union. 
The wood of the graft, does not at all descend below its original 
place of junction with that of the stock ; which, immediately 
below, wholly retains its native character ; and, in the part where 
both are spliced together, each constantly extends itself in the 
direction of the divergent laminae of its silver grain. The heart- 
wood also appears to increase by lateral extension ; but I am 
ignorant of the channels through which the additional matter is 
conveyed to it. 
I will now take the liberty to trespass on your patience, by 
