A Method for Determining Tracheid Lengths in Petrified Wood by Analysis of Cross Sections

A method is presented for estimating the length of tracheids in fossilized secondary xylem by analysis of intersected cells in cross sections. A two-dimensional model depicting cell position in wood is used to derive an equation which relates the total tracheid length to the length of the tracheid apex and the ratio between the number of intersected tracheid shafts and apices observed in cross section. Use of the technique is demonstrated in an investigation of the wood of Sphenophyllum plurifoliatum, an anatomically preserved Carboniferous arthrophyte with extremely long tracheids. The values obtained in the analysis correspond closely to lengths determined by indirect measurement. An examination of the assumptions on which the method is based reveals that the accuracy of the cell length estimates will vary according to the shape of area being analysed and intrinsic structural features of the wood.