Conductance in the wood of selected Carboniferous plants

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Abstract
Specific conductance was calculated for secondary xylem in seven Carboniferous stem taxa utilizing an equation derived from the Hagen-Poiseuille relation. Arborescent and lianoid representatives of major pteridophytic (Calamitaceae, Lepidodenraceae, Sphenophyllaceae) and gymnospermous (Cordaitaceae, Medullosaceae) groups were examined. In the calamite Arthropitys communis and the seed plant Cordaites (Cordaixylon sp. and Mesoxylon sp.), conductance corresponded approximately to the low end of the range for both extant conifers and angiosperms. A substantially higher conductance was determined for the wood of Arthropitys deltoides, conforming to the high end of the range for conifers and the low-middle part of the range for angiosperms. The highest conductance values were found in Sphenophyllum plurifoliatum, Medullosa noei, and Paralycopodites brevifolius and corresponded to the middle-high portion of the range for vessel-containing angiosperms. This outcome is particularly significant in light of the fact that tracheary elements in the fossils are imperforate. The results indicate that conductance in secondary xylem of some of the most ancient, woody groups was comparable to that in extant plants and that highly effective conducting tissue developed relatively early in plant evolution. Moreover, it is suggested that the general relationship between wood anatomy, growth habit, and ecology demonstrated for living plants can also be extended back in time to include fossil plants.