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Wood Anatomy of Onagraceae: Further Species; Root Anatomy; Significance of Vestured Pits and Allied Structures in Dicotyledons
Annals of the Missouri Botanical Garden
Vol. 69, No. 4, Studies in Onagraceae (1982), pp. 755-769
Published by: Missouri Botanical Garden Press
Stable URL: http://www.jstor.org/stable/2398995
Page Count: 15
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Quantitative and qualitative features are described for Circaea lutetiana subsp. canadensis, Fuchsia decidua, Lopezia suffrutescens, Oenothera deltoides subsp. howellii, and six species of Ludwigia. Comparison is made between secondary xylem of stem wood and that of tuberous roots for Fuchsia decidua; the roots have narrow, angular vessels with scalariform lateral wall pitting in a ground tissue of starch-rich parenchyma indistinguishable from ray cells. Succulent roots of Xylonagra show the same features. Wood anatomy for the species studied is interpreted in terms of habit and ecology; features relating to herbaceous modes of structure are discussed since all of the species studied can be termed subshrubs or small to large herbs. A discussion of the systematic distribution of vestured pits is presented. Allied phenomena (warty surfaces in conifer tracheids, warty surfaces in vessel elements some of which are intercontinuous with warts of vestured pits, grooves in vessel walls, and helical thickenings on vessel walls) are considered in conjunction with vestured pits. Experimental data available is minimal, so little evidence other than systematic distribution and occurrence within cell types can be adduced at present. These forms of wall relief seem to occur essentially only in conducting cells. Four hypotheses are entertained: (1), vestured pits as a means of preventing pit membrane rupture in pit aspiration; (2), wall relief as a means of lowering resistance to water flow; (3), wall relief as a mechanism for mending of air embolisms; and (4), wall relief as a means of increasing hydration (bonding of water to wall), thereby enabling high water tensions during drought or frost but lessening likelihood of cavitations. Although all hypotheses are considered possible in terms of today's limited knowledge, the fourth hypothesis is considered the most likely by virtue of systematic, ecological, and cell type occurrence of wall relief types.
Annals of the Missouri Botanical Garden © 1982 Missouri Botanical Garden Press