These examples suffice to illustrate the general appearance presented by the vegetative shoots of recent species of which the foliage leaves vary considerably—from the small scale-leaves of _Lycopodium tetragonum_, to the very slender linear subulate leaves of such a species as _L. verticillatum_ Linn. or the long and broader lamina of _L. Dalhousianum_ (fig. 121, E). It is obvious that fragments of the various types preserved as fossils might well be mistaken either for some of the larger mosses or for twigs of conifers. As Dr Bommer[94] has pointed out in his interesting paper on “Les causes d’erreur dans l’étude des empreintes végétales” some dicotyledonous plants may also simulate the habit of Lycopods: he cites _Phyllachne clavigera_ Hook (Candolleaceae), _Tafalla graveolens_ Wedd (Compositae) and _Lavoisiera lycopodioides_ Gard. (Melastomataceae). Another point illustrated by fig. 121 is the close agreement in habit and in the form of the leaves and leaf-cushions between the recent plants and the Palaeozoic Lepidodendreae. In his masterly essay “On the vegetation of the Carboniferous Period, as compared with that of the present day” Sir Joseph Hooker called attention to the variation in the shape and arrangement of the leaves in the same species of _Lycopodium_. The three woodcuts which he publishes of _Lycopodium densum_, a New Zealand species, afford striking examples of the diversity in habit and leaf-form and justify his warning “that if the species of _Lepidodendron_ were as prone to vary in the foliage as are those of _Lycopodium_, our available means for distinguishing them are wholly insufficient[95].”