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the Ascent of the Sap in Trees. 
to every other kind of wood. In sawing this tree into boards, 
it is usual to cut it, as much as possible, into what are called 
quarter boards ; which are so named because the tree is first cut 
into quarters. In a perfect board of this kind, the saw exactly 
follows the direction in which the tree most readily divides when 
cloven : in this case, the laminee of the silver grain lie parallel 
with the surface of the board ; and a board thus cut, when pro- 
perly laid in the floor, is rarely or never seen to deviate from 
its true horizontal position. If, on the contrary, one be sawed 
across the silver grain, it will, during many years, be incapable 
of bearing changes of temperature, and of moisture, without be- 
ing warped ; nor will the strength of numerous nails be suffi- 
cient entirely to prevent the inconvenience thence arising. That 
surface, of a board of this kind, which grew nearest the centre of 
the tree, will always shew a tendency to become convex, and 
the opposite one concave, if placed in a situation where both 
sides are equally exposed to heat and moisture. You may pro- 
bably have observed, that when an oak has been deprived of its 
bark, and exposed to the sun and air, its surface has been every 
where covered with small clefts. These are always formed by 
the laminae of the silver grain having parted from each other ; 
and they will long continue to open and close again with the 
changes of the weather. In the last summer, I very frequently 
placed pieces of oak, recently deprived of its bark, in a situation 
where it was fully exposed to the sun, but defended from rain. 
The surface of the tree, in a few hours, presented a great num- 
ber of small clefts, into which I put, in the middle of the day, 
the points of small iron pins. Examining these late in the even- 
ing, I found that the wood closed so much as to hold them 
firmly ; and, early in the next morning, they were not easily 
mdccci. Y y 
