Telome theory
The telome theory describes the formation of the complex morphological structure of the land plants from simply constructed, algae resembling so-called Urlandpflanzen . Founder of this very influential theory to explain evolutionary changes during the early phase of plant land settlement was in 1930 Walter Zimmermann .
As telome (singular: telome ) he referred to the at best slightly differentiated, unbranched sections of the first land plants. A teloma is therefore an axially shaped basic organ and, according to Zimmermann, begins at the base of the branch of another teloma and ends apically either at the tip of the shoot or at another branch.
The telome theory is based on the analysis of fossils . It is based on the assumption the that corm (ie especially today's land plants roots , stems , leaves and Sporangienstände ) through five "elementary processes" (Zimmermann) can be derived from Urlandpflanzen, known as a fossil of Rhynia may have resembled:
- Peaking : Of the previously almost symmetrical-forked, i.e. equally branching and always skyward-oriented rungs, one became longer and stronger than the other, so that a differentiation into main and secondary shoots emerged.
- Planation : Previously arranged three-dimensional bars were moved in groups into one level .
- Adhesion : The groups of rungs, which had already been shifted into one level by planing, were connected to one another by connective tissue ( parenchyma ) ; this concerned both the organs later to be designated as leaf and as main and minor axis ("trunk" and "branch").
- Reduction : The side shoot, which was smaller due to over-peaking, was - interpretable as extreme over-peaking - shortened so much that only a single, unbifurcated shoot was left.
- Curvature : Individual terminal telomas (shoot sections after the last branch) curved downwards and ultimately became the seat of the sporangia .
The teloma theory formulated by Zimmermann in 1930 is still credited today with the fact that actually observed stages of development are summarized in a phylogenetically plausible scheme. However, this applies above all to the conditions in fully grown plants, during whose ontogeny was hardly included in the theory. There are reservations about the applicability of his theory, especially with regard to the evolution of angiosperms , which Zimmermann wanted to derive from so-called "Urtelomstands".
See also
literature
- Walter Zimmermann: History of Plants Thieme, Stuttgart 1949 (2nd revised edition. Deutscher Taschenbuch-Verlag, Munich 1970 ( dtv 4043 Scientific series )).
- Walter Zimmermann: Phylogenie der Pflanzen G. Fischer, Stuttgart 1959 (2nd edition).
- Walter Zimmermann: The telom theory (= progress in evolution research 1). G. Fischer, Stuttgart 1965.