Ontogeny of the vascular system of Botrychium multifidum (S. G. Gmelin) Rupr. (Ophioglossaceae) and its bearing on stelar theories
1980
STEVENSON, D.W.
Basipetal to the shoot apex, a procambial ring with parenchymatous gaps is present. The protoxylem poles are endarrh in both the ectophloic siphonostele and the collateral vascular bundle which comprises the leaf trace. Each leaf trace has an anastomosing system of protoxylem poles that decreases in number basipetally from five to three to two. Differentiation of the leaf trace procambium and protoxylem is bidirectional, that is the differentiation first occurs near the base of the leaf and acropetally in the leaf and basipetally in the stem. Then a fascicular cambium differentiates betweem the primary xylem and phloem in the leaf. This vascular cambium which is also present in the stem is unidirectional and only produces secondary xylem centripetally. Limited secondary growth also occurs in roots. Medullary tracheids when present are longitudinally continuous with the vascular system. The stele of the stem is interpretated as a sympodium of leaf traces and the pith is considered to be fundamental tissue enclosed by the anastomosing of leaf traces.
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