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DEVELOPMENTAL DYNAMICS OF ARBORESCENT LYCOPHYTES—APICAL AND LATERAL GROWTH IN STIGMARIA FICOIDES
Author(s) -
Rothwell Gar W.,
Pryor Janelle S.
Publication year - 1991
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1991.tb14538.x
Subject(s) - tracheid , apex (geometry) , meristem , biology , xylem , cambium , vascular cambium , anatomy , thickening , botany , morphology (biology) , biophysics , paleontology , materials science , shoot , polymer science
Meristematic activity in Stigmaria ftcoides is interpreted from a combination of historical information and newly developed data on stelar diameter, wood production, and morphology of the apex. Many specimens of Stigmaria preserved as mold/casts display little or no recognizable change in the width of the stelar groove between successive forks. Thickness of the xylem cylinder in permineralized axes of similar diameters also is relatively uniform. Over a distance of 1.5 m along one axis the mean number of tracheids per radial row diminishes from 56 to 46 toward the apex. While this is a statistically significant decrease, in biological terms it is consistent with the reduction in primary growth that one would expect in a zone of apoxogenesis. Coupled with our knowledge of the morphology of the apex, these data allow us to interpret radially aligned tracheids in the steles of most stigmarian axes as having been produced largely from the action of a primary thickening meristem, rather than from a secondary vascular cambium as commonly believed.