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Pteridospermous Plants from the Pennsylvanian of Illinois and Missouri

Chester A. Arnold and Waldo E. Steidtmann
American Journal of Botany
Vol. 24, No. 9 (Nov., 1937), pp. 644-650
Stable URL: http://www.jstor.org/stable/2436646
Page Count: 7
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Pteridospermous Plants from the Pennsylvanian of Illinois and Missouri
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Abstract

Myeloxylon missouriensis, a structurally preserved petiole of the Medullosae, is distinct from the two previously described medullosan petioles from America. The peripheral sclerenchyma zone is narrow, and the strands are separated by intrusions of ground tissue. Scattered throughout the ground tissue are gum canals and collateral vascular bundles, the latter possessing tracheids of the closely wound spiral type. The phloem, in most instances, has disappeared, and the remaining cavities are filled with black structureless material. The walls of the cells throughout the petiole appear abnormally thickened by mineral accretion. Rotodontiospermum illinoense is a structurally preserved seed intimately associated with medullosan remains. It is characterized by the presence of a fibrous, deeply furrowed endotesta. The double vascular system and the free nucellus indicate affinity with the Trigonocarpales. A specimen of Crossotheca sagittata, from Mazon Creek, Illinois, shows sporangia arranged in a similar manner to those of C. Boulayi, and hence different from the arrangement as originally figured. All the material described is of middle Pennsylvanian age.

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