VII - On the factors that influence external form of fossil plants; with descriptions of the foliage of some species of the Palaeozoic Equisetalean Genus Annularia Sternberg

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Abstract
I — On the Factors which Influence the External Form of Fossil Plants Most writers of general treatises on Palaeobotany give an introductory chapter on fossilization, and this as a rule includes an account of the various kinds of fossil plants and the circumstances under which plants may become incorporated in sediments. The differences between the external form of the fossil and the original plant fragment are not often mentioned in relation to the factors which operate in the production of a fossil. It is often implied that fossil plants of the “ incrustation ” or “ impression ” type are produced in much the same way as herbarium specimens. That such a crude analogy does not satisfactorily explain the forms found among fossil plants of this type is obvious to those who have applied transfer methods to the examination of such fossils. In the writer’s opinion, the reason why so little precision has been given to descriptions of fossil-plant forms is that insufficient attention has been paid to the properties of sediments and the role played by the matrix. While many writers recognize that the differences in shape between a fossil and the original plant are due to the compressibility of the plant tissues the writer is not aware of any reference in the literature to the importance of the compressibility of the matrix in determining the form of a fossil embedded in it. It will be shown that the alteration in shape of a plant in undergoing fossilization in many cases may be best described as the result first of the collapse of the plant tissues and second of a more or less uniform vertical strain of the fossil and the surrounding matrix together.