_Selaginella_ differs from _Lycopodium_ in the production of two kinds of spores, megaspores and microspores, and, in the great majority of species, in the dimorphic character of the foliage leaves, which are usually arranged in four rows, the laminae of the upper rows being very much smaller than those of the lower (fig. 130, 1–3). The smaller leaves are shown more clearly in fig. 130, 1_a_. It is obvious from an examination of a Selaginella shoot, such as is shown in fig. 130, that in fossil specimens it would often be almost impossible to recognise the existence of two kinds of leaves. Some species, _e.g._ _Selaginella spinosa_[113], the sole British representative of the genus, are homophyllous and agree in this respect with most species of _Lycopodium_. Another feature characteristic of _Selaginella_, as contrasted with _Lycopodium_, is the presence of a ligule in both foliage leaves and sporophylls. This is a colourless thin lamina attached by a comparatively stout foot to the base of a pit on the upper surface and close to the lower edge of the leaf (fig. 130, 4, _l_; fig. 131, E, F, _l_). [Illustration: FIG. 130. _Selaginella grandis._ (1–3, nat. size.)] In an erect species, such as _S. grandis_ Moore[114] (fig. 130 and fig. 131, G) from Borneo, the main shoots, which may attain a height of 2–3 feet, bear small and inconspicuous leaves of one kind, but the lateral and repeatedly forked shoots are heterophyllous. The passage from the homophyllous to the heterophyllous arrangement is shown in the transition from the erect to the dorsiventral habit of the lateral shoots (fig. 130, 2). The monopodially or dichotomously branched shoots produce long naked axes at the forks; these grow downwards to the ground where they develop numerous dichotomously forked branches. For certain reasons these naked aerial axes were named rhizophores and have always been styled shoots, the term root being restricted to repeatedly forked branches which the rhizophores produce in the soil. It has, however, been shown by Professor Harvey-Gibson[115] that there is no sufficient reason for drawing any morphological distinction between rhizophores and roots, the term root being applicable to both.