mesarch


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mesarch

[′me‚zärk]
(botany)
Having metaxylem on both sides of the protoxylem in a siphonostele.
(ecology)
Originating in a mesic environment.
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References in periodicals archive ?
The primary vasculature is non-sympodial, and primary xylem only occurs as the downward extension of mesarch leaf traces (Fig.
Axes showing endarch maturation and a sympodial vasculature have been classified as Cordaixylon, while those with mesarch leaf traces and a non-sympodial vasculature, as seen in the Joggins specimen (Fig.
2006) stated that the xylem is usually mesarch in the shoot of Monilophytes (including Eu- and Leptosporangiate ferns).
Eleven character states change on the branch subtending Biscalitheca + Corynepteris: #5, growth form of stem/axis erect [right arrow] rhizomatous; #7, arborescence present [right arrow] absent; #24, scales absent [right arrow] present; #35, protoxylem of stem/axis mesarch [right arrow] exarch; #41, radial rachis/axis trace round-elliptical [right arrow] absent; #57, meio/microsporangium bearing structure unlike vegetative [right arrow] somewhat modified from the vegetative; #61, abaxially attached sporangia absent [right arrow] present; #65, meio/microsporangial grouping absent [right arrow] present; #71, sporangial stalk absent [right arrow] broad; #74, functional annulus absent [right arrow] present; and #88, exospore surface nearly smooth or plain [right arrow] obviously sculptured.
Among the fossil forms, Fascivarioxylon (Jain, 1962), of the Jurassic of India, has a vascular cylinder with mesarch, bicollateral centrifugal-centripetal bundles, with uniform secondary growth in both directions; and Stem B, found in the Argentinian Cretaceous, has inverse bundles inside the first vascular cylinder.