WITH regard to the succession of races which have undergone a complete specific change through successive geological periods, we have not in plants, in as far as I am aware, any such cases of “true linear types or forms which are intermediate between others because they stand in a direct genetic relation to them,” as Professor Huxley appears to have made out in favour of the pedigree of the horse in his last anniversary address to the Geological Society. And I may, in regard to plants, repeat with still greater emphasis his dictum, that “it is no easy matter to find clear and unmistakable evidence of filiation among fossil animals; for in order that such evidence should be quite satisfactory, it is necessary that we should be acquainted with all the most important features of the organisation of the animals which are supposed to be thus related, and not merely with the fragments upon which the genera and species of the palæontologist are so often based.” The difficulty is much greater in the case of fossil plants; for instead of bones, teeth, or shells, portions of internal or external skeletons, the parts preserved to us from the Tertiary period are generally those least indicative of structural organisation. Mr. Carruthers has recently (Geological Magazine, April and July 1869, and Journal of the Geological Society, August 1869) adduced satisfactory evidence of the close affinity of Sigillaria and the allied genera of the coal-period with the living Lycopodiacere, formerly suggested by Dr. Hooker, but, as he informs me, no connecting links, no specimens indeed of the whole order, have as yet been found in any of the intermediate Cretaceous or Tertiary deposits. Among the latter the presence of numerous types, to which we may plausibly refer as to the ancestors of living races, is established upon unimpeachable data; but I have been unable to find that a single case of authentic pedigree, as successively altered from the Cretaceous through the abundant deposits of the Eocene and Miocene period to the living races, has been as yet as satisfactorily made out as that of the absolute identity of Taxodium and others above mentioned, although I feel very little doubt that such a one will yet be traced when our palaeontologists will have ceased to confound and reason alike upon the best proved facts and the wildest guesses. Our late distinguished foreign member, Professor Unger, whose loss we have had so recently to deplore, had indeed, shortly before his death, published, under the name of “Geologie der Europaischen Waldbaume, part I. Laubholzer,” no less than twelve tabular pedigrees of European forest races; but it seems to me that in this, as in another of the same eminent palaeontologist's papers to which I shall presently have to refer, his speculations have been deduced more freely from conjectures than from facts. There is no doubt that the presence of closely allied representatives of our Beeches, Birches, Alders, Oaks, Limes, & c., in the Tertiary deposits of central and southern Europe is fully proved by inflorescences and fruits as well as leaves; but how can we establish the successive changes of character in a race when we have only the inflorescence of one period, the fruit of another, and the leaf of a third? I do not find a single case in which all three have been found in more than one stage, and by far the great majority of these fossil species are established on the authority of detached leaves or fragments of leaves alone.
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BENTHAM, G. On the Progress of Botany in 1869. Nature 2, 110–113 (1870). https://doi.org/10.1038/002110a0