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

Patterns of water movement in intact and excised stems of Fraxinusamericana L. and Acer saccharum Marsh. seedlings were delineatedwith periodic acid-reduced basic fuchsin staining techniqueand microscopy. In intact Fraxinus stems water movement occurredprimarily in the large early-wood vessels of the current xylemincrement except in the current shoot where the ring porouscharacter was not developed and water movement occurred in largevessels scattered throughout the xylem. In intact Acer stemswater movement occurred in large vessels in the current annualring and in the outer two-thirds of the prior-year annual ring.The pattern of water movement in excised stems under suctionwas similar to the pattern in stems of intact transpiring Fraxinusplants, whereas in Acer a larger portion of the cross-sectionalarea of stems was used when suction was applied to excised stems.Relative conductivity was similar for the two species as a resultof conduction in Fraxinus in a small number of large-diametervessels and in Acer in a large number of small-diameter vessels.