Though fertilization by an externally produced male nucleus has not been definitely proved there is probability that, in some instances, the fruit may be the product of sexual fusion. There are however a number of genera and species in which the development is apogamous so far as any external copulation is possible and the sporiferous tissue seems to be a purely vegetative product up to the stage of ascus formation. In _Phlyctis agelaea_ Krabbe[610] found abundant apothecia developing normally and not accompanied by spermogonia; in _Phialopsis rubra_ studied also by him the primordium arises among the cells of the periderm on which the lichen grows, and he failed to find any trace of a sexual act. In his elaborate study of Gloeolichens Forssell[611] established the presence of carpogonia with trichogynes in two species—_Pyrenopsis phaeococca_ and _P. impolita_, but without any appearance of fertilization; in all the others examined, the origin of the fruit was vegetative. Wainio[612] records a similar observation in a species of _Pyrenopsis_ in which there was formed a spiral ascogonium and a trichogyne, but the latter never reached the surface. Neubner[613] claimed to have proved a vegetative origin for the asci in the Caliciaceae; but he overlooked the presence of spermogonia and his conclusions are doubtful. Fünfstück[614] found apogamous development in _Peltigera_ (including _Peltidea_) and his results have never been disputed. The ascogonial cells are surrounded at an early stage by a weft of vegetative hyphae. No trichogynes are formed and spermogonia are absent or very rare in the genus, though pycnidia with macrospores occur occasionally. Some recent work by Darbishire[615] on the genus supplies additional details. The apothecial primordium always originated near the growing margin of the thallus, where certain medullary hyphae were seen to swell up and stain more deeply than others. These at first were uninucleate, but the nuclei increased by division as the cells became larger, and in time there was formed a mass of closely interwoven cells full of cytoplasm. “No coiled carpogonia can be made out, but these darkly stained cells form part of a connected system of branching hyphae coming from the medulla further back.” Long unbranched multi-septate hyphae—evidently functionless trichogynes—travelled towards the cortex but gradually died off. Certain of the larger cells—the “ascogonia”—grew out as ascogenous hyphae into which the nuclei passed in pairs and finally gave rise to the asci.