Fig. 7. Procedure to determine the vessel length. (a) A segment of approximately the probable length of the given species vessels is cut from the stem of interest and bark is removed from its basal end. (b) A rubber tubing of a suitable, tight-fitting diameter is slipped over the segment’s debarked end, and a relatively large (e.g. 50 mL) air-filled syringe is attached to the free end of this tubing. With the syringe’s plunger a mild, above-atmospheric air pressure is generated within the tubing while holding the segment’s free end under water. If bubbles emerge from that end, at least one vessel has been cut at both ends of the segment, allowing air to move freely through the segment’s entire length (if no bubbles emerge, proceed as described below). Repeat this test using progressively longer stem segments until one is found from which bubbles do not emerge under pressure. From this segment, cut off successively shorter slices and, after each cut, retest the segment, until bubbles are first seen to emerge. The segment’s length at this point is just shorter than the length of its longest vessel. If, however, no bubbles emerge from the first stem segment that is tested, the stem’s longest vessels are shorter than that segment’s length, so relatively long pieces must be cut successively from it until bubbles do emerge. Then a segment slightly longer that this (but one that does not emit bubbles when first tested) can be used to come close to the maximum vessel length as at the end of the foregoing procedure.