Biomedical subjects

B Meyer-Berthaud

Publications and source records attributed to B Meyer-Berthaud.

3 recordsLinked to original sources

PubMed2000

Computer simulation of sphenopsid architecture. I. Principles and methodology.

The modelling system AMAP 1 provides morphological models that reproduce the series of shapes developed in a plant structure during its growth. It is applicable to plants that have architectural features consistent with the principles introduced by Hallé et al. (Hallé, F., Oldeman, R.A.A., Tomlinson, P.B., 1978. Tropical Trees and Forest. Springer, Berlin, 441 pp.). We present the main principles of the methodology including the use of an architectural template and the statistical processing of the data collected on sample plants and a description of its components and parameters. We use models of Equisetum telmateia aerial shoots as examples of adaptations of this methodology to plants represented by a limited number of specimens. The main features of this approach that make it especially relevant for modelling incomplete and fragmented fossil plants include the use of architectural templates constructed by adding discrete morphological entities limited to a number of axial components as follows: as many branch orders as are identified in the sample plants, a single extension unit per branch order, and its internodes. This approach is viewed as a means to provide visual representations of plants at different ontogenetical stages, expressing our current knowledge of their growth and branching strategies, and of the parameters that control their geometries.

Journal Article↗

PubMed2000

The development of Archaeopteris: new evolutionary characters from the structural analysis of an Early Famennian trunk from southeast Morocco.

A 5 m long trunk of a young Archaeopteris/Callixylon erianum tree from the Late Devonian of Morocco shows new branching patterns for early lignophytes. This progymnosperm tree produces a helical pattern of traces that we infer belonged to reduced, short-lived, primary (apical) branches (type A) as well as two types of adventitious traces (types B and H). We infer that type-B traces supplied branches that initiate close to the site of attachment on the trunk of some, but not all type-A branches in an irregular but nonrandom pattern. Unlike ephemeral type-A branches, those of type B persist and become long-lived, potentially permanent units of the architecture of Archaeopteris trees. Type-H adventitious traces are also short-lived and occur singly or in serial groups, but differ from traces of either type A or B branches by lacking differentiation into a readily identifiable organ category. We interpret type-H traces as supplying latent primordia that could develop into either adventitious roots or shoots depending on extrinsic factors. Our new data suggest that Archaeopteris had a wide range of branch primordium amplitude. Type-B branches compare with axillary lateral branch buds of some Early Carboniferous spermatophytes (Calamopitys) and are a major developmental departure from the strictly apical, pseudomonopodial shoot branching of older aneurophyte progymnosperms. Type-H traces suggest that Archaeopteris trees had some potential for formation of adventitious roots or shoots in response to environmental factors, such as partial burial by overbank sedimentation. Collectively, these novel methods of tree branching may partly explain the extraordinary success and worldwide dominance of Archaeopteris forests on fluvially dominated, Late Devonian floodplains.

Journal Article↗

PubMed2000

[The first trees. The Archaeopteris model].

The earliest self-supporting organisms exceeding 2 m in height evolved about 370 million years ago, approximately 100 million years after the rise of the first land plants. Evidence for the tree habit is usually indirect and assessed from the diameter of the available stem fragments. Four systematic groups of Devonian plants evolved the tree habit independantly: the Lycopsida, Cladoxylopsida, and progymnosperms in the Middle Devonian, the Equisetopsida in the Late Devonian. All share a free-sporing life cycle which limits their habitats to wet areas. Their branching pattern involves the strict division of their apices, whether equally or unequally. The progymnosperm genus Archaeopteris was widespread worldwide and evolved the highest trees of the Devonian (maximum height estimated at 40 m). Besides it ecological significance as the dominant component of the earliest forests, Archaeopteris currently represents the closest known relative to the seed plants with which it shares two derived characters, the heterosporous life cycle, and the possession of leaves. Another distinctive feature of Archaeopteris trees is represented by the double function of their wood for both support and conduction. New analyses involving vascular trace analysis in anatomically preserved specimens have demonstrated that Archaeopteris is not the simple tree reconstructed by Beck (1962). In this fate model, Archaeopteris consisted of an erect trunk bearing short-lived, flattened, leaf-like branch systems forming a terminal crown. New evidence indicates that laterally to these appendages of apical origin, a new type of branches, of adventitious origin, evolved which development compares to that of the axillary branches of the seed plants. These branches which were large and long-lived represent major architectural components of the tree. Evidence for vascular structures comparable to those produced on stem cuttings in modern plants suggest that Archaeopteris may have evolved vegetative strategies for propagation. The set of "modern" characters of Archaeopteris may explain its success until the Devonian/Carboniferous boundary when its extinction is correlated to the radiation of the earliest seed plants.

Biological Evolution↗