LEAF VENATION OF ANGIOSPERMS - FORM AND EVOLUTION

Leaf venation patterns are caused by the interaction of genetically determined processes, environmental effects and chance. The ''rules'' of geometry are explained as a means of using energy economically. The major contribution of self-organizational processes can be deduced from a topological description. The similarity of the venation system for some orders of magnitude can be measured as fractality, using a scaling exponent. Observations of the physiological anatomy also show connections with transport activity. Vein systems of the angiosperm type developed for the first time during the Permian/Triassic periods, in connection with major climatic changes on earth. The important contribution of self-organization to the development of the pattern of small veins resulted in a higher adaptability and was a key advance in angiosperm evolution.