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No description available.

No description available.

No description available.

The bulk of the material which forms the basis of this communication was placed in the writer's hands for investigation by Prof. P. W. Oliver. And I gladly take this opportunity of expressing my deep indebtedness to him for much helpful advice and criticism and also for putting at my disposal for examination such slides of the University College Collection as I have had occasion to consult. My thanks are also due to Dr. D. H. Scott and to Prof. F. E. Wells for the loan of preparations of this seed. To Dr. Scott I am also indebted for permitting me to examine the more important sections in his unique collection of Trigonooarpus Parkinsoni, without which an adequate comparison between the two seeds would not have been possible. A full description of the new seed is embodied in the following pages together with a consideration of its relationships and the theoretical questions to which its structure gives rise. In the former connection the organisation of Trigonocarpus Oliveri is reconsidered and good reasons are shown for its exclusion from that genus. The same methods have been employed in the reconstruction of the present seed as were used in the investigation of Conostoma oblongum and C. anglo-germanicum. These have been recently described by the writer and need not be recapitulated here. In order to facilitate reference the same general plan of arrangement has been adopted as has been employed in other recent papers dealing with fossil seeds.

The secondary wood formed by cambial activity in the growth of trees records with varying degrees of precision the amount of seasonality and other aspects of the climate under which it grew. A survey is presented of the extent to which this climatic 'data-store' can be directly 'read back', based on the extensive literature on the environmental control of wood formation in modern plants. This led to the investigation of growth ring characters in selected fossil and recent wood in the course of which a cyclic phenomenon, apparently under endogenous control, was demonstrated. The potential of this information to deduce aspects of the palaeoclimate from fossil wood (of age extending back some 370 million years) is then considered. Attention was directed particularly to three intervals of geological time, namely the Upper Devonian, the Permo-Carboniferous and the later Mesozoic in which growth ring characteristics present features of particular interest. A classification of growth ring features is developed and five categories are defined. Some of these data are derived from direct observation of fossil wood material by the author and some from the literature. Growth ring characteristics are plotted on palaeo-reconstruction maps and the climatic significance is considered in relation to other indicators of palaeo-climate. Consideration is given to the phenomenon of tree growth (and very substantial increments) in high latitudes during two phases of geological time---the Permian and the later Mesozoic. At these times major forest growth evidently extended far beyond the present latitudinal range. Consideration of the radiation energy input at high latitudes, and the effect of a generally more isothermal global climate suggests that these growth ring phenomena can be explained in uniformitarian terms without the need to invoke shift in axial inclination or similar processes as some, have advocated.

The mechanisms and processes that lead to the formation of a plant compression fossil have been experimentally reproduced and studied in the present investigation. This research has used two main lines of investigation: firstly, experimental modelling of the fossilisation process; and secondly, a detailed examination of plant compression fossils. Early experimental modelling was based on the simplest system possible. A dry compression apparatus was used in which artificial materials, representing plant and matrix, were subjected to vertical deformation. Forms were produced which closely resembled vertical sections of Sawdonia, Stigmaria, Calamites and Lepidodendron. Further apparatus was subsequently constructed, in which wet sediment and actual plant material were compressed, thus more closely reproducing the natural system of compacting sediment. Using this apparatus, factors, such as the role of grain size, change in dimensions of the plant organ, and rigidity of plant tissues were investigated. A recirculating laboratory flume tank was used to examine the flow conditions, and other parameters that were required to produce burial of plant material and in-fill of hollow stems. The results obtained formed a basis for interpreting the conditions of formation of observed fossil stem infills. Experimental compression of the stems buried in the flume indicated the effect of an infill on the eventual form of the fossil. Examination of plant compression fossils in the present investigation has been mainly based on a study of vertical sections through the matrix. These reveal the overall structure of the compression, and the processes leading to its formation. The Carboniferous plants, Cyperites, Alethopteris, Lepidostrobus and Trigonocarpus, have been investigated in this way. An understanding of the factors that dictate the final form of the fossil, using the techniques described above, gives new insight into the fossilisation process. This is of potential value in reconstructing plants from fossils only known in the compression state of preservation. This is illustrated with reference to Permian ovulate glossopterid fructifications from Gondwanaland. Computer modelling provides an alternative method for studying the compression process, and an account is given of a computer-based investigation of the deformation process.

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Paul E. Beckmann and Bruce R. Musicus. / Includes bibliographical references (leaves 54-55). / Research supported in part by the Draper Laboratories. DL-H-404158 Research supported in part by a Rockwell Doctoral Fellowship. Research supported in part by the Advanced Research Projects Agency, monitored by the Office of Naval Research. N00014-89-J-1489

Detailed descriptions of 3-D anatomically preserved specimens in paleobotany have been undertaken for over 100 years. Some of the most comprehensively characterised of these specimens are reproductive structures, especially cones and ovules. Throughout this time many of the ways of gaining information such specimens has remained static. In recent years new computer software and techniques have been developed that allow detailed 3- D computer reconstructions to be undertaken that allow holistic observations of the context of the whole organ. Detailed 3-D reconstructions have been undertaken of several genera of Palaeozoic and Mesozoic paleobotanical reproductive organs. These complex structures have undergone traditional preparation, such as serial sectioning, preparation specifically for reconstruction such as serial grinding and non-destructive scanning micro X-ray tomography. Reconstructions were then produced in bespoke software, Serial Paleontological Image Editing and Rendering System (SPIERS). The reconstructions produced provide a new understanding to the structure and functions of tissues within paleobotanical reproductive specimens. For the first time, specimens of extinct and extant genera have been compared using new reconstruction techniques in order to aid in the future understanding of their evolution and development, and to aid visualisation of complex structures for which illustrations in 2-D form are inadequate.