The bionomics of Palaeozoic plants is a subject worthy of more serious attention than it has so far received. The search for morphological characters that may have facilitated the wanderings of widely distributed genera and species and a closer investigation of physiological-anatomical problems presented by the vegetative organs of petrified plants would not only extend our knowledge of the morphology of ancient types but would stimulate comparative study and, incidentally, relieve the dullness of pure description. It may be argued that we should first establish a more solid foundation by further observations on living plants; but even at the risk of allowing speculation too free a hand the attempt is worth making, and it may be urged that, as in phylogenetic enquiries so in other branches of botany, facts obtained from plants of other ages may serve to supply deficiencies in knowledge based only on existing forms. One of the difficulties inseparable from the study of fossil plants, namely the identification of impressions and casts with specimens exhibiting anatomical characters, is particularly well illustrated by seeds. The description of a genus based on mere external form may sometimes be extended without great risk of error to include species founded on anatomical characters, but on the other hand, there are many instances in which—despite a general resemblance in form and size between petrifactions and impressions—lack of evidence of generic identity requires the employment of distinctive names. The determination of impressions is, as Lesquereux recognised, ‘subject to a great deal of uncertainty,’ and many of the genera founded on external features are purely artificial and include species that have no essential features in common. Moreover in the case of petrified specimens the apparent absence of an external fleshy layer is often due to destruction before preservation: as Solms-Laubach[801] points out, it is obviously impossible to be certain as to the number of integumental layers in seeds that are not well preserved in all their parts. Goeppert founded a new genus, _Acanthocarpus_, on a Permian seed described as _A. xanthioides_[802], because of the occurrence of spinous processes attached to an obcordate kernel: these apparent spines are in all probability the remains of a very imperfectly preserved sarcotesta. The preservation of the central portion of a seed, that is the seed-cavity with the enclosing shell, conveniently called the nucule, has often led to an unnecessary multiplication of generic terms. Other examples of confusion resulting from different states of preservation are quoted in the accounts of some of the selected types.