In most heteromerous lichens, however, the origin of the paraphyses is exclusively vegetative: they arise as branches from the primordial complex that forms the covering hyphae of the ascogonium both above and below. Schwendener[581] had already pointed out the difference in origin between the two constituents of the hymenium in one of his earlier studies on the development of the apothecium, and this view has been repeatedly confirmed by recent workers, except by Wahlberg[582] who has insisted that they rise from the same cells as the asci, a statement disproved by Baur[583]. The paraphyses originate not only from the covering hyphae, but from vegetative cells in close connection with the primordium. In this mode of development, lichens diverge from fungi, but even in these a vegetative origin for the paraphyses has been pointed out in _Lachnea scutellata_[584] where they branch from the hyphae lying round the ascogonium. There is no general rule for the order of development. In _Lecanora subfusca_ Baur[583] found that vertical filaments had reached the surface by the time the trichogyne was formed, and their pointed brown tips gave a ready clue to the position of the carpogonia. In _Lecidea enteroleuca_[585] they show their characteristic form and arrangement before there is any trace of ascus formation. In _Solorina_[585] they are well formed before the ascogenous hyphae appear. In other lichens such as _Placodium saxicolum_[586], _Peltigera rufescens_[587] and _P. malacea_[587] the two systems—paraphyses and ascogonium—grow simultaneously, though in _P. horizontalis_ the ascogonium has disappeared by the time the paraphyses are formed. In the genus _Nephroma_, in _Physcia stellaris_ and in _Xanthorina parietina_ the paraphyses are also late in making their appearance. In most instances, the paraphyses push their way up between the cortical cells which gradually become absorbed, or they may stop short of the surface as in _Nephromium tomentosum_[587]. The overlying layer of cortical cells in that case dies off gradually and in time disappears. Such an apothecium is said to be “at first veiled.” Later formed paraphyses at the circumference of the apothecium form the parathecium, which is thus continuous with the hypothecium. _e._ VARIATIONS IN APOTHECIAL DEVELOPMENT. Lichens are among the least stereotyped of plants: instances of variation have been noted in several genera.