_Cones._ The terminal portions of the branches of _Selaginella_ usually bear smaller leaves of uniform size which function as sporophylls, but in this genus the fertile shoots do not generally form such distinct cones as in many species of _Lycopodium_. In _S. grandis_ (figs. 130, 3; 131, G) the long and narrow strobili consist of a slender axis bearing imbricate sporophylls in four rows: each sporophyll subtends a sporangium situated between the ligule and the axis of the shoot. The sporangium may be developed from the axis of the cone or, as in _Lycopodium_, from the cells of the sporophyll[126]. In some species the lower sporophylls bear only megasporangia, each normally containing four megaspores, the microsporangia being confined to the upper part of the cone. This distribution of the two kinds of sporangia is, however, by no means constant[127]: in some cases, _e.g._ _S. rupestris_, cones may bear megasporangia only, and in the cone of _S. grandis_, of which a small piece is represented in fig. 131, G, all the sporangia were found to contain microspores. The occurrence of two kinds of spores in _Selaginella_ constitutes a feature of special importance from the point of view of the relationship between the Phanerogams, in which heterospory is a constant character, and the heterosporous Pteridophytes. One of the most striking distinctions between the Phanerogams and the rest of the vegetable kingdom lies in the production of seeds. Recent work has, however, shown that seed-production can no longer be regarded as a distinguishing feature of the Gymnosperms and Angiosperms. Palaeozoic plants which combined filicinean and cycadean features resembled the existing Phanerogams in the possession of highly specialised seeds. This discovery adds point to the comparison of the true seed with structures concerned with reproduction in seedless plants, which in the course of evolution gave rise to the more efficient arrangement for the nursing, protection, and ultimate dispersal of the embryo. In the megaspore of _Selaginella_ we have, as Hofmeister was the first to recognise in 1851, a structure homologous with the embryo-sac of the Phanerogam. The embryo-sac consists of a large cell produced in a mass of parenchymatous tissue known as the nucellus which is almost completely enclosed by one or more integuments. Fertilisation of the egg-cell within the embryo-sac takes place as a rule while the female reproductive organ is still attached to the parent-plant and separation does not occur until the ovule has become the seed.