A Century Of Wood Anatomy and 75 Years Of IAWA
Carlquist, Sherwin .
Unexpected Patterns of Bordered Pit Occurrence in Wood Prefaced by Some Perspectives on Where Comparative Wood Anatomy Has Been and Therefore Might Be Going.
BORDERED pits occur in walls of living ray cells of numerous species of woody dicotyledons. Occurrence of this feature has been minimally reported because the pits are relatively small and not easily observed in face view. Using a small sampling from the hundreds of species from which conclusions were drawn, bordered pits are illustrated in sectional view with light microscopy and with scanning electron microscopy (SEM) in face view for dicotyledonous and gnetalean woods. Bordered pits are more numerous and have more prominent borders on tangential walls of procumbent ray cells, but they also occur on radial walls; they are about equally abundant on vertical and horizontal walls of upright cells, suggesting parallels to cell shape in flow pathway design. Axial parenchyma typically has secondary walls thinner than those of ray cells, but bordered pits may be found in some species on cross walls of parenchyma strands. A large number of simple pits is often present in a cross wall of parenchyma strand. There is no apparent phylogenetic correlation between phylogenetic position of species and presence of borders in ray cells or axial parenchyma. Bordered pits represent a compromise between maximal mechanical strength and maximal conduction. High rates of flow of sugar solutions may occur if starch in ray cells or axial parenchyma is mobilized for sudden osmotic enhancement of the conductive stream or for rapid development of foliage, flowers, or fruits. Measurement of secondary wall thickness of ray cells may offer simple inferential information about the role that rays play in mechanical strength of woods. Axial parenchyma cells are mechanically less significant than ray cells.
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1 - Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California, 93105-2199, USA
Presentation Type: Symposium or Colloquium Presentation
Date: Tuesday, August 1st, 2006
Time: 4:45 PM