In the genus _Cladonia_, differentiation of the generative hyphae may take place at a very early stage. Wainio[417] observed, in _Cl. caespiticia_, a trichogyne in a still solid podetium only 90µ in height; usually they appear later, and, where scyphi are formed, the carpogonium often arises at the edge of the scyphus. Baur[418] and Wolff[419] have furnished conclusive evidence of the late appearance of the carpogonium in _Cl. pyxidata_, _Cl. degenerans_, _Cl. furcata_ and _Cl. gracilis_: in all of these species carpogonia with trichogynes were observed on the edge of well-developed scyphi. Baur draws the conclusion that the podetium is merely a vertical thallus, citing as additional evidence that it also bears the spermogonia (or pycnidia), though at the same time he allows that the apothecium may have played an important part in its phylogenetic development. He agrees also with the account of the first appearance of the podetium as described by Krabbe, who found that it began with the hyphae of the gonidial zone branching upwards in a quite normal manner, only that there were more of them, and that they finally pierced the cortex. Krabbe also asserted that in the early stages the podetia were without gonidia and that these arrived later from the open as colonists, in this contradicting Wainio’s statement that gonidia were carried up from the primary thallus. It seems probable that the podetium—as Wainio and Baur both have stated—is homologous with the apothecial stalk, though in most cases it is completely transformed into a vertical thallus. If the view of their formation from the gonidial zone is accepted, then they differ widely in origin from normal branches in which the tissues of the main axis are repeated in the secondary structures, whereas in this vertical thallus, hyphae from the gonidial zone alone take part in the development. It must be admitted that Baur’s view of the podetium as essentially thalline seems to be strengthened by the formation of podetia at the centre of the scyphus, as in _Cl. verticillata_, which are new structures and are not an elongation of the original conceptacular tissue. It can however equally be argued that the acquired thalline character is complete and, therefore, includes the possibility of giving rise to new podetia. The relegation of the carpogonium to a position far removed from the base or primordium of the apothecium need not necessarily interfere with the conception of the primordial tissue as homologous with the conceptacle; but more research is needed, as Baur dealt only with one species, _Cl. pyxidata_, and Gertrude Wolff confined her attention to the carpogonial stages at the edge of the scyphus.