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Journal Article

Some Characters of Xylem Tissue in Cycads

H. B. Sifton
Botanical Gazette
Vol. 70, No. 6 (Dec., 1920), pp. 425-435
Stable URL: http://www.jstor.org/stable/2470031
Page Count: 13

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Topics: Tracheids, Pitting, Petioles, Fossils, Wood structure, Xylem, Plant tissues, Phylogenetics, Botany, Plants
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Abstract

1. A study of the primary and secondary wood of Cycads indicates the development of reticulate, alternate, and opposite pitting directly from scalariform types. 2. The grouped, uniseriate, and scattered pitting characteristic of higher forms is shown to be formed by the elimination of pits. In low forms, of which the Cycads are a type, this elimination proceeded without apparent order, forming all types of grouping indiscriminately. 3. Similar arrangements of pits occur in Cordaites, although its type has become more fixed than is the case in the Cycads. 4. The Cycads, like the Araucarians, have more primitive types of pitting at the ends of tracheids and where they come in contact with parenchyma. 5. The xylem of certain of the Cycads quite commonly exhibits spiral tertiary thickenings. 6. Bars of Sanio of the Araucarian type are found in both primary and secondary Cycad wood. An elongated type of bar is also present. The Araucarian type is considered the most primitive in living seed plants. No explanation of its origin is offered by Bailey's theory. 7. Trabeculae are present. This work was done with the advice of Professor R. B. Thomson. I am indebted to him, not only for advice and encouragement, but also for the supply of materials necessary for the work.

Notes and References

This item contains 11 references.

Literature Cited
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  • 2
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    PENHALLOW, D.-P., North American Gymnosperms. 1907.
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    SCOTT, D. H., Studies in fossil botany. 2d ed. 1909.
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    SEWARD, A. C., and FoRD, S. O., The Araucarieae, recent and extinct. Phil. Trans. Roy. Soc. London. B.198:305-4II. 1906.
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    SIFTON, H.B., On the occurrence and significance of "bars" or "rims" of Sanio in the Cycads. BOT. GAZ.60:400-405. 1915.
  • 11
    THOMSON, R. B., On the comparative anatomy and affinities of the Arau- carineae. Phil. Trans. Roy. Soc. London. B.204:1-50. 1913.