Don Kaplan - his legacy: Influencing teaching and research
Hagemann, Wolfgang .
Comparative Morphology or the Typological Method to Understand Plant Form and its Evolution.
Plants are open organisms, exposing directly their surfaces to the environment for water, gas, and energy supply. Therefore, the perception of plant form is prerequisite for understanding plant histology, not vv. Plant tissue is phragmoblastemic, the result of the evolution of cell division which has changed from "cytokinesis" into "phragmotomy". Primary morphogenesis becomes accomplished in promeristems, which are the blastozones, i.e. apical blastozones and marginal blastozones of leaves, thalli of liverworts, and fern gametophytes. Roots lack blastozones because of their endogenous growth beyond the blastozones. Blastozones become fractionated equally or unequally in differently formed fractions. This occurs under the influence of groundtissue differentiation, not cell differentiation. The leaf marginal blastozones are fractions of the shoot blastozone periphery being thus primarily dorsiventral.
A type is defined by its construction elements and the positional relations between them, e.g. the cormus type by groundorgans: shoot axis, lateral leaves, and endogenous roots. To understand the evolution of such a type, one needs knowledge of the preceding types and their options for transformation. Beyond that typologists will perceive types of different categories. Troll discerned two categories: the „Organisationstypus" (organization type) and the „Gestalttypus" (form type), e.g. the organization type of a flower as is a metamorphous, closed shoot, and a form type is the flower-like head of the Asteraceae resulting from the organization type of an open racemic florescence. I shall use a third category of types, the "life types" representing haploid and diploid generations of a species together. A discussion of the phylogenetic relations between liverworts and ferns will have to consider typological relations between the involved categories of types. The method of typology will be demonstrated at hand of this example.
1 - University of Heidelberg, Heidelberg, 69120, Germany
Presentation Type: Symposium
Location: Ballroom 2 (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 10:15 AM