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Journal Article

Vascular Tissues of Microcycas Calocoma

Mintin A. Chrysler
Botanical Gazette
Vol. 82, No. 3 (Nov., 1926), pp. 233-252
Stable URL: http://www.jstor.org/stable/2470641
Page Count: 23

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Topics: Tracheids, Xylem, Phloem, Plants, Genera, Plant cells, Tree trunks, Parenchyma, Pith, Sieve tubes
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Vascular Tissues of Microcycas Calocoma
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Abstract

1. An extension of the range of Microcycas is noted, recording the occurrence of a station on the lowlands. 2. The trunk differs from that of Dioon in having conspicuous and persistent external rings composed of leaf bases separated by wider spaces occupied by scales. 3. The xylem of the stem consists typically of pitted tracheids, but there is a remarkably wide inner zone of scalariform elements representing a juvenile stage. 4. The scalariform zone shows some indication of division into a few growth rings. 5. Protoxylem is definitely present in the stem. It is endarch, and consists of narrow tracheids with close spiral and reticulate thickenings, followed by scalariform elements of increasing diameter. 6. The leaf traces are persistent, and become secondarily attached to the later formed tracheids of the woody cylinder, establishing a connection between the inner and outer wood. 7. The phloem of the different organs varies as to presence of bast fibers. A phylogenetic significance is attributed to this. 8. Pith bundles with inverse orientation occur sporadically. 9. A small amount of centripetal xylem is found in the peduncle of the microsporangiate cone. 10. A consideration of the various features leads to the conclusion that Microcycas is a distinctly advanced genus.

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