Patterns of Water Movement in Intact and Excised Stems of Fraxinus americana and Acer saccharum Seedlings1

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Abstract
Patterns of water movement in intact and excised stems of Fraxinus americana L. and Acer saccharum Marsh. seedlings were delineated with periodic acid-reduced basic fuchsin staining technique and microscopy. In intact Fraxinus stems water movement occurred primarily in the large early-wood vessels of the current xylem increment except in the current shoot where the ring porous character was not developed and water movement occurred in large vessels scattered throughout the xylem. In intact Acer stems water movement occurred in large vessels in the current annual ring and in the outer two-thirds of the prior-year annual ring. The pattern of water movement in excised stems under suction was similar to the pattern in stems of intact transpiring Fraxinus plants, whereas in Acer a larger portion of the cross-sectional area of stems was used when suction was applied to excised stems. Relative conductivity was similar for the two species as a result of conduction in Fraxinus in a small number of large-diameter vessels and in Acer in a large number of small-diameter vessels.