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ESTABLISHMENT OF THE VASCULAR SYSTEM IN SEEDLINGS OF POPULUS DELTOIDES BARTR.
Author(s) -
Larson Philip R.
Publication year - 1979
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.1537-2197.1979.tb06245.x
Subject(s) - phyllotaxis , biology , cotyledon , hypocotyl , primordium , seedling , botany , xylem , stipule , meristem , shoot , biochemistry , gene
Seven seedlings ranging from 1 to 25 days old were embedded in Spurr's resin and serially sectioned at 1–2 μm. Sectioning extended from well above the apex downward to the hypocotyl base in the 1–day seedlings and to varying levels in the hypocotyl in the older seedlings. Procambial development was analyzed in its entirety for each seedling, and a composite two‐dimensional diagram representing the procambial system of a 25‐day‐old seedling was prepared. Each cotyledon was served by a double‐trace, one‐half of which was derived from each of two embryonic bundles. The central traces serving the four primary leaves were in turn derived from the four cotyledonary bundles comprising the double traces. The procambial system serving the cotyledons and the four primary leaves approximated a decussate phyllotaxy. The central traces serving the secondary leaves were arranged in a helix that conformed at first to a 1/3 and then to a 2/5 phyllotaxy. Transitions to higher phyllotactic orders were systematic and reproducible, and they occurred in an orderly sequence in both the central and lateral leaf traces. The manner in which leaf traces diverged from parent traces to serve new leaf primordia provided for vascular redundancy. Thus, the entire vascular system was integrated into a highly functional whole.