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Journal Article

Stem Anatomy of Dioon spinulosum

LaDema M. Langdon
Botanical Gazette
Vol. 70, No. 2 (Aug., 1920), pp. 110-125
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Page Count: 19

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Topics: Tracheids, Seedlings, Leaves, Cylinders, Plant cells, Girdles, Petioles, Plant growth, Tree trunks, Phloem
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1. The medullary rays of Dioon spinulosum are of three distinct types: uniseriate rays, a single layer of cells wide and several cells deep; multiseriate rays, two to several cells in width and of variable longitudinal extent; and broad foliar rays or leaf gaps, which, with their included leaf traces, are such a constant feature of this wood. 2. The fibrovascular elements constituting the leaf traces in the foliar rays and connecting these traces with the secondary wood are peculiar, irregular scalariform tracheids which in the course of their development curve gradually downward through the ray, until they become inserted between the perpendicular fibrous elements of the main stele. 3. The regular pitted elements of the secondary xylem are also often diverted to one side into a direction parallel to that of the trace. 4. Both the scalariform and the pitted elements constituting these traces, in their peculiar manner of enlargement and elongation, furnish excellent illustrations of gliding growth. 5. For each leaf or scale leaf 7-9 strands (the number varying with the size of the leaf base) separate from the vascular cylinder. The two inner ones, arising from the proximal side of the central cylinder, pursue a more or less direct vertical course into the ventral part of the petiole; the rest of the traces, leaving the stem cylinder at different points, pass obliquely upward into the cortex and the sheathing base of the leaf, where an anastomosis of traces takes place, resulting in the two characteristic girdles. 6. The two direct strands entering the ventral or abaxial part of the leaf may also unite with the two dorsal girdling strands at the base of the petiole, so that the whole system is reducible in the older seedlings and adult stem to two main horizontal strands with their associated lateral traces.

Notes and References

This item contains 13 references.

Literature Cited
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    WORSDELL, W. C., The anatomy of the stem of Macrozamia compared with that of other genera of Cycadeae. Ann. Botany10.: 601-620. 1896.
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    — The comparative anatomy of certain species of Encephalartos Lehm. Trans. Linn. Soc.24:445-459. 1899.