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COPYRIGHT 2005 Acedemia Colombiana de Ciencias Exactas, Fisicas y Naturales
Resumen
Este articulo trata sobre el metodo morfologico comparativo (tipologia) combinado con estudios de desarrollo para mejorar el conocimiento de las relaciones filogeneticas entre diversas formas de plantas. El metodo se ilustra con dos ejemplos; el primero alude a las relaciones filogeneticas existentes entre las hepaticas y los helechos, casi todos de tipo- repens abierto. El segundo ilustra la relacion mas compleja existente entre las angiospermas primitivas, tipo arbol, las cuales retornaron a la condicion de arbusto o hierba perenne y aun a la de plantas delgadas tipo-repens abierto. El tipo del sinflorescencia caracteristica de las angiospermas desempena un papel central en este desarrollo aun si se suprime esta ultima etapa.
Palabras clave: tipogenesis, plantas.
Abstract
The presented paper deals with the comparative morphological method (typology) combined with developmental studies as a means for understanding phylogenetic relations between different plant forms. This method becomes illuminated by two examples. The first are the phylogenetic relations between liverworts and ferns from which many follow the open repens-type. The second illuminates the much more complicated relations' between the primitive, tree-like angiosperms which returned via shrubs and herbal perennial plants to the delicate plants of the open repens-type. The angiospermic synflorescence-type plays a central role in this evolutionary pathway even if it becomes relinquished by the last step.
Key words: plants, typogenesis.
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Classic comparative plant morphology, as Wilhelm Troll left us behind in his magnificent work, needs more attention and further critical development to play its essential role in modern biology. This should be done in steady exchange with those experimental sciences to which typology provides the organismic basis. Comparative morphology allows not only a first insight into the relations between the organisms of a common type, but has beyond that the capacity to give insight into the relations between different types, i.e. to find out the different pathways for possible typogeneses. The so-called synthetic theory of evolution denies this (see Reif et al. 2000). But in my opinion this theory is indeed in many respects insufficient to solve especially macroevolutionary problems as long, as the organisms are seen only as objects of environmental influences, i.e. mutation and selection as the factors driving evolution (Weingarten, 1993:280). The typological construction cannot be changed in any direction, but only in such a way that life of the modified organism is warranted. This makes the organism a subject in evolution, which offers only certain developmental options for constructive changes. The knowledge of these allows to predict possible typogeneses (Hagemann, 2000). Therefore, the organism, which is the entity of life, must be placed in the center of biology for understanding typogenesis.
Another correction of the theoretical fundaments of plant biology is also urgently needed, namely the classic cell theory, which estimated cells of higher plants as its "elementary organisms" (Brucke, 1861, Sitte 1998:2, 36). So-called land plants, such as bryophytes, pteridophytes, and seed plants, have a phragmoblastemic structure. I introduced the term "phragmoblastem" for the type of tissue of all these plants (Hagemann, 1982, 1992). It expresses that cell divisions in land plants produce by no means individualized living units, as the term "elementary organistas" suggests. Instead of this, cell division means the integration of new cell walls into the growing plant organism. This integration becomes realized by the phragmoplast, which becomes etsablished by the persisting spindle apparatus together with a dense ER-network between the daughter nuclei after mitosis. The remaining spindle elements are further used for transport of Golgivesicles containing the wall materials. They become fused on the periphery of the centrifugally growing cell plate and this again conserves thousends of plasmodesmata passing the cell plate (Fig. 1). On the one hand, the protoplast permeating the wall system of the whole plant, behaves as a unit, as is on the other hand the wall skeletton of the plant. Thus, cell division in higher plants provides subdivision without interrupting the organismic unit. This is the solution of the problems occuring with organismic growth.
[FIGURA 1 OMITIR]
The vegetation body of small primitive land plants has an open, frondose, dorsiventral, and polar structure, such as those of Metzgeriales, e.g. Pellia epiphylla or the gametophytes of ferns, such as Stenochlaena tenuifolia (Figs. 3-4). They represent, what I have called the open, frondose repens-type, an evergrowing and everdying plant creeping endlessly over the ground (Hagemann 1999, 2000; Fig. 2). Such an organism expresses its polarity by its growing pole and dying pole. The first is represented by the blastozone, the second by its necrozone (Hagemann & Gleissberg, 1996). Blastozones are those parts of apical meristems which are responsible for primary morphogenesis, i.e. the establishment of the primary organismic form elements of the plant body. The frondose thallus is formed by a marginal blastozone growing horizontally. It forms under the influence of gravity a leaflike structure with different dorsal and ventral sides. Prevailing thickening growth of the central blastozone forms a winged midrib. The polarity between the blastozone and the necrozone together with gravity, light, and water supply engenders a lot of differences between the poles, dorsal and ventral sides, photosynthesis and storage sites. The resulting gradients cause transport of substances (moving of materials) between sources and sinks, such as water transport in the wall system between the ventral and the transpiring dorsal side. Metabolites move between photosynthetic active tissues on the light exposed, adult dorsal side and the blastozones, meristems and storage sites as the sinks for those products. Thus, tissue differentiation is the consequence of certain claimes to organismic regions. Those effects, which dominate local tissues, cause their specific differentiation, e.g. transport of metabolites cause procambium differentiation, and later vascular bundles with more specialized transporting tissues. The organism, not the single cell, decides on tissue differentiation by special usage of certain tissue zones in the growing organism.
[FIGURA 2-4 OMITIR]
After the establishment of the primary form, the tissue of the blastozone -the promeristem (Sussex & Steeves, 1967, Esau, 1977:272, Saehs, 1991:131)--enters a phase of accelerated growth with the effect of declining cell dimensions in the so-called transition zone Popham, 1951, Esau, 1965:96, Stevenson, 1976). Within the transition zone tissue differentiation begins with the establishment of the primary histogenes, as are the protoderm, procambium, and the quickly extending groundhistogen (Sachs, 1991:131) which produce during further growth the final tissue organization of the adult vegetation body (final histogenesis: Hagemann 1999). In our gametophytic examples inner histogenetic differentiation stays in a simple condition without the differentiation of procambium, which may occur in other examples of Metzgeriales, such as Metzgeria, Pallavicinia or Hymenophytum (Hagemann, 1999). But in Pellia...
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