form
places of least resistance in the walls. In hardwoods such as
oak, chestnut, ash, etc., buckling occurs only in the
thinnest-walled elements, such as the vessels, and not in the
true fibres.

According to Jaccard[6] the folding of the cells is accompanied
by characteristic alterations of their walls which seem to split
them into extremely thin layers. When greatly magnified, these
layers appear in longitudinal sections as delicate threads
without any definite arrangements, while on cross section they
appear as numerous concentric strata. This may be explained on
the ground that the growth of a fibre is by successive layers
which, under the influence of compression, are sheared apart.
This is particularly the case with thick-walled cells such as
are found in late wood.

[Footnote 6: Jaccard, P.: Etude anatomique des bois comprimes.
Mit. d. Schw. Centralanstalt f.d. forst. Versuchswesen. X. Band,
1. Heft. Zurich, 1910, p. 66.]

|-------------------------------------------------------|
| TABLE VI |
|-------------------------------------------------------|
| RESULTS OF ENDWISE COMPRESSION TESTS ON SMALL CLEAR |
| PIECES OF 40 WOODS IN GREEN CONDITION |
| (Forest Service Cir. 213) |
|-------------------------------------------------------|
| | Fibre | | Modulus |
| COMMON NAME | stress at | Crushing | of |
| OF SPECIES | elastic | strength | elasticity |
| | limit | | |
|-------------------+-----------+----------+------------|
| | Lbs. per | Lbs. per | Lbs. per |
| | sq. inch | sq. inch | sq. inch |
| | | | |
| Hardwoods | | | |
| | | | |
| Ash, white | 3,510 | 4,220 | 1,531,000 |
| Basswood | 780 | 1,820 | 1,016,000 |
| Beech | 2,770 | 3,480 | 1,412,000 |
| Birch, yellow | 2,570 | 3,400 | 1,915,000 |
| Elm, slippery | 3,410 | 3,990 | 1,453,000 |
| Hackberry | 2,730 | 3,310 | 1,068,000 |
| Hickory, | | | |
| big shellbark | 3,570 | 4,520 | 1,658,000 |
| bitternut | 4,330 | 4,570 | 1,616,000 |