Seeds are abundantly represented as fossils from Carboniferous to Post-Tertiary deposits. The importance of fossil and sub-fossil species in the later geological series has been demonstrated by the investigations of Mr and Mrs Clement Reid and a few other workers in this neglected field. In cases where it is possible to assign seeds to their parent-plants the descriptions of casts, impressions, or petrifactions are added to the account of vegetative organs; but it frequently happens that seeds are preserved only as detached specimens many of which have little or no value as botanical records, while others that afford striking examples of the possibilities of petrifaction as a means of preserving the most delicate structures, are of great importance. In Volume +ii.+ an account was given of such Palaeozoic seed-bearing organs as _Lepidocarpon_ and _Miadesmia_, and the genera _Lagenostoma_, _Sphaerostoma_, and _Trigonocarpus_ are dealt with in this volume under _Lyginopteris_, _Heterangium_, and _Medullosa_. Certain seeds afford some evidence as to the systematic position of the parent-plants though insufficient to warrant more than a surmise as to the nature of the vegetative organs: in several cases it is only from the resemblance of detached seeds to types that on the strength of more or less convincing evidence are referred to definite parent-plants that any conclusions can be drawn with regard to precise systematic position. In view of the occurrence of several different types of seeds that retain their morphological features, but cannot be assigned with any degree of certainty to genera founded on vegetative organs, a special chapter is devoted to a comparative study of selected examples with the object of directing attention to data bearing on evolutionary problems. The chief interest of Palaeozoic seeds to the botanist lies in the facts they contribute towards the elucidation of questions connected with the promotion of the megasporangium and megaspore of the Pteridophyta to the higher stage represented by the integumented megasporangium (nucellus) and single megaspore that in the main fulfil the definition of a seed[790]. ‘With the evolution of the seed,’ as Oliver says, ‘the plant rose at a bound to a higher plane, and this structure in its perfected form has become the very centre of the plant’s existence[791].’ We can as yet form a very partial conception of the successive stages in the adoption of the seed-habit, but since 1855, the year in which Hooker and Binney[792] published their paper on the structure of _Trigonocarpus_, ample proof has been furnished of the importance of Palaeozoic seeds from the standpoint of affinity between recent Gymnosperms and extinct seed-bearing plants, and of the _modus operandi_ of evolutionary tendencies. A cursory examination of Palaeozoic seeds suffices to demonstrate their resemblance to those of recent Cycads and the seed of _Ginkgo biloba_; but while it is clearly with these Gymnosperms