Michael A. Cichan

Wood-borings in Premnoxylon: plant-animal interactions in the carboniferous

Cichan, M. A. and Taylor, T. N., 1982. Wood-borings in Premnoxylon: Plant--animal interactions in the Carboniferous. Palaeogeogr., Palaeoclimatol., Palaeoecol., 39: 123--127. A complex system of anastomosing burrows is described from structurally preserved Lower--Middle Pennsylvanian Premnoxylon wood. The burrows are filled with small uniformly shaped coprolites. This discovery represents the oldest recorded evidence for the existence of wood-boring organisms, and indicates that a relatively specialized form of plant--animal interaction was present during the late Paleozoic. It also provides additional support for the idea that Premnoxylon, a cordaitean root, was an aerial organ.

Vascular Cambium and Wood Development in Carboniferous Plants. II. Sphenophyllum plurifoliatum Williamson and Scott (Sphenophyllales)

Wood development and cambial activity in the Carboniferous articulate stem Sphenophyllum plurifoliatum Williamson and Scott were studied by analyzing mature interfascicular secondary xylem. The wood parenchyma is interpreted as being a true vascular-ray system. Rays are mostly biseriate and appear as groups of cells in the interstices between tracheids. Ray cells are longitudinally elongate, and some exhibit radial processes that extend between tracheids. The radial arrangement of the ray cells was apparently disrupted by tracheid enlargement during wood development. A distinct pattern of tracheid enlargement from inner to outer wood is apparent, suggesting that the fusiform initials increased in size during secondary growth. There is no evidence for multiplicative division of fusiform initials, and the increase in cambial circumference seems to have been accommodated primarily by fusiform initial enlargement. The absence of a mechanism to augment the number of fusiform initials in Sphenophyllum implies limited lateral growth, thus providing additional evidence that the vascular cambium was determinate. The results of this investigation, in conjunction with those of earlier work on Carboniferous lycopods, suggest that the vascular cambium in woody pteridophytes was fundamentally different from that of modern seed plants.

THE ULTRASTRUCTURE OF MESOZOIC POLLEN:PTERUCHUS DUBIUS (THOMAS) TOWNROW

Taylor, T.N., Cichan, M.A. and Baldoni, A.M., 1984. The ultrastructure of Mesozoic pollen: Pteruchus dubius (Thomas) Townrow. Rev. Palaeobot. Palynol., 41: 319--327. Pollen grains extracted from a specimen of Pteruchus dubius (Thomas) Townrow 1962 collected from Middle Triassic sediments (Molteno beds?) are examined at the ultrastructural level. The vesiculate grains possess sacci that are slightly inclined toward the distal surface and covered with delicate perforations. The cappus region is poorly developed proximally, and a narrow sulcus on the distal surface marks the probable site of germination. The sporoderm is thin and endoreticulations on saccus walls are either lacking or poorly defined. Ultrastructural features of the grains are compared with other late Paleozoic and Mesozoic types.

A Systematic and Developmental Analysis of Arthropitys deltoides Sp. Nov.

Arthropitys deltoides sp. nov. is described from Pennsylvanian sediments of southeastern Kentucky The axes are characterized by parenchymatous interfascicular rays that broaden conspicuously toward the periphery of the wood and secondary tracheids with diameters that are more than twice as large as any yet described in Arthropitys In addition, there is a well-developed rhytidome composed of several concentric periderm lamellae. The species is compared with other late Paleozoic calamites that possess persistent interfascicular rays, and the differences between them are described. Based on the presence of broad parenchymatous zones in the wood, large-diameter thin-walled tracheids, and the relatively small size of the axes, it is suggested that A deltoides was a liana An analysis of the secondary xylem reveals that there is a marked ontogenetic increase in the size of the secondary rays and the width of the individual parenchyma cells The data suggest that analyses of this type are important in distinguishing between developmental and taxonomic variation and that such an approach may prove useful in characterizing individual calamite species and, ultimately, in assessing systematic relationships within this group.

Ultrastructural studies of in situ Devonian spores: Protobarinophyton pennsylvanicum Brauer

This investigation examines sporoderm ultrastructure in Protobarinophyton pennsylvanicum Brauer (Barinophytaceae), a Devonian vascular plant that produced both large and small spores in the same sporangium. The sporoderm of the small spores is approximately 1.0 μm thick, with irregular gaps in the wall near the outer surface. In the large spores, the sporoderm is approximately 6.5 μm thick and is divided into an unornamented surface layer and a broad, alveolate inner layer. In view of the significant and consistent structural differences in the walls of the spores, it is suggested that the small spores represent microspores and not immature or aborted large spores. The general pattern of sporoderm organization in the two spore types is comparable to that reported previously for Barinophyton citrulliforme, and, more importantly, it is similar to that found in microspores and megaspores of extant heterosporous plants. This similarity suggests that Protobarinophyton pennsylvanicum, like modern heterosporous plants, produced spores that formed endosporic sexually differentiated gametophytes and provides a foundation for suggesting a more precise, biological definition of the term “heterospory” in fossil plants. In this context, sex determination in this unusual Devonian vascular plant is discussed, and it is suggested that the sex of the spores is determined by nutritional factors.

On the structure and morphology of the seed Pachytesta muncii N. SP. (Medullosales)

Cichan, M.A. and Taylor, T.N., 1981. On the structure and morphology of the seed Pachytesta muncii n. sp. (Medullosales). Rev. Palaeobot. Palynol., 34: 359--367. A new species of the pteridosperm seed Pachytesta is described from sediments of the Lower Pennsylvanian of Kentucky. The seed is approximately 3.0 cm long and 2.0 cm wide at the mid-level. The integument consists of a broad sarcotesta with twelve peripheral vascular bundles, a fibrous sclerotesta of variable thickness, and a narrow endotesta which is poorly preserved. Fibrous trabeculae, which are continuous with the sclerotesta, traverse the commissured primary ribs in the upper third of the seed. Anatomically, Pachytesta muncii n. sp. is most similar to P. vera, differing only with respect to overall size, degree of integumentary vascularization, and general histology of the nucellar stalk. It is suggested that P. muncii was produced by the seed fern Medullosa anglica on the basis of their common occurrence at the Lewis Creek coal ball locality.