108, pp.

52 _et seq._] (1) Knots do not materially influence the stiffness of structural timber.
(2) Only defects of the most serious character affect the elastic limit of beams.

Stiffness and elastic strength are more dependent upon the quality of the wood fibre than upon defects in the beam.
(3) The effect of knots is to reduce the difference between the fibre stress at elastic limit and the modulus of rupture of beams.

The breaking strength is very susceptible to defects.
(4) Sound knots do not weaken wood when subject to compression parallel to the grain.[34] [Footnote 34: Bul.

115, U.S.Forest Service: Mechanical properties of western hemlock, p.