The reproductive organs or spores borne on the fronds of a fern produce, on germination, a thin green structure, known as the prothallus, less than an inch in length: this bears the sexual organs, and as the result of the union of the male and female cells, the embryo fern-plant begins its existence as a parasite on the inconspicuous prothallus, until after unfolding its first green leaf and thrusting a slender root into the ground, it starts its career as an independent organism[2]. In this life-cycle the seed plays no part. [2] The life-history of a Fern is clearly described by Prof. Bower in a recent volume in this series. It is noteworthy that the absence of any indication of spore-capsules and spores, in the case of some of the supposed fern leaves from the Coal-measures, caused some suspicion in the mind of an Austrian Palaeobotanist as to the right of such specimens to be classed among the ferns. This opinion, based in the first place on negative evidence and but little regarded by other authors, has in recent years been proved correct. In 1904 a paper was read before the Royal Society by Professor Oliver and Dr Scott(43) in which evidence was brought forward pointing to the conclusion that one of these generalised plants bore true seeds. Subsequently Dr Kidston published an account of some specimens of another of these Palaeozoic plants in which was actually shown an organic connexion between undoubted seeds and pieces of a fern-like frond(44). Without entering into further details, these and similar discoveries may be summarised as follows:--Many of the supposed Fern-fronds of Palaeozoic age, particularly those characteristic of the Coal-measures, are the leaves of plants which in their anatomical characters combined features now shared by true Ferns and by the Cycads. The reproductive organs of these Palaeozoic genera differed widely from those of existing ferns; the male organs, while not unlike the spore-capsules and spores of certain ferns, recall the male organs of living Conifers and Cycads, and the female organs were represented by seeds of a highly complex form. These seed-bearing plants have been called Pteridosperms, a name which expresses the combination of fern-like features with one of the distinguishing attributes of the higher plants, namely the possession of seeds. The ancestors of Pteridosperms are as yet unknown; it is, however, reasonable to assume that there existed in some pre-Carboniferous epoch a group of simple plants from which both Ferns and Pteridosperms were derived. In the forests of the Coal age true Ferns probably occupied a subordinate position in relation to the Pteridosperms.