Current trends in paleobotany

The remarkable growth of paleobotany within recent years is revealed in the expanded body of literature and by the increase in number of languages in which it is written. New techniques are involved in the use of cuticles and the electron microscope.Precambrian rocks, once regarded as essentially without fossils, have been found to contain a variety of micro-organisms, and compounds believed to be decomposition products of chlorophyll have been identified in rocks three billion years old.Some new ideas have developed concerning the morphology and relationships of some of the very old vascular plants. The original reconstruction of Psilophyton embodied more than one plant, and Asteroxylon now appears to be a lycopod. The Hyeniales and Pseudosporochnus belong to the Cladoxylales. Archaeopteris and Callixylon are the foliage and woody trunks of the same plant which has been designated a "progymnosperm". Seeds now appear to have been recognized in the Upper Devonian, and a considerable number of primitive seeds have lately been found in the Lower Carboniferous calciferous sandstone.Decreased coal mining has curtailed the supply of Carboniferous compressions. In North America outstanding progress has been made in the study of petrified plants in coal balls.Studies of the Glossopteris flora have been extended into Antarctica. Continental drift seems to be the only hypothesis that satisfactorily explains the position of the fragments of ancient Gondwanaland at the present time.Reinvestigations of the inflorescences of Cycadeoidea have shown that the structure of the staminate disc was originally misinterpreted. It is a complex synangium that encircles the gynoecium, rather than being a whorl of pinnate stamens.The occurrence of angiosperm leaves in the Lower Cretaceous of Greenland is questioned. Some investigators now believe that angiosperms originated at high altitudes in the tropics during the Permian Period. Others would derive them from the Glossopteridae during the same period. Fruits and seeds have proved quite useful in accurate determination of Tertiary angiosperms. Petrified woods create special problems in identification and nomenclature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33240/1/0000631.pd