A detailed analysis of selected quantitative features was made of secondary xylem from the trunk, branch, and root of a specimen of Robinia pseudoacacia L. The analysis serves as a basis for interpreting two suites of fossil woods closely similar to the wood of Robinia. One assemblage had its provenance in western Nevada and the other in southern California. Results of the survey show considerable overlap in ranges of variation in the fossils and extant woods. These findings parallel results of a similar investigation by Matten et al. (1977). Woods from both fossil localities fall within the specifications of the organ species Robinia zirkellii (Platen) Matten, Gastaldo ' Lee. The survey also revealed the kinds of differences that may be found in species of Robinia growing in dissimilar habitats. Differences noted among trunk, branch and root wood of extant Robinia make it possible to distinguish these organs among the fossils.
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