(See Fig.

22.) [Illustration: FIG.

23 .-- Cross section of longleaf pine showing several growth rings with variations in the width of the dark-colored late wood.

Seven resin ducts are visible.

X 33.
_Photomicrograph by U.S.Forest Service_] If one compares a heavy piece of pine with a light specimen it will be seen at once that the heavier one contains a larger proportion of late wood than the other, and is therefore considerably darker.