_Lecanora subfusca_ and allied species which have a thin thallus are frequently overgrown by this _Pertusaria_ and a dark line generally precedes the invading lichen; the hyphae and the gonidia of the _Lecanorae_ are first killed and changed to a brown structureless mass which is then split up by the advancing hyphae of the _Pertusaria_ into small portions. A little way back from the edge of the predatory thallus the dead particles are no longer visible, having been dissolved and completely used up. _Pertusaria amara_ also may overgrow _Lecanorae_, though, generally, its onward course is checked and deflected towards a lateral direction; if however it is in a young and vigorous condition, it attacks the thallus in its path, and ahead of it appears the rather broad blackish line marking the fatal effect of the enzyme, the rest of the host thallus being unaffected. Neither _Pertusaria_ seems to profit much, and does not grow either faster or thicker; the thallus appears indeed to be hindered rather than helped by the encounter. _Biatora_ (_Lecidea_) _quernea_ with a looser, more furfuraceous thallus is also killed and dissolved by _Pertusariae_; but if the _Biatora_ is growing near to a withering or dead lichen it, also, profits by the food material at hand, grows over it and uses it up. Bitter has also observed lichens overgrown by _Haematomma_ sp.; the growth of that lichen is indeed so rapid that few others can withstand its approach. Another common rock species, _Lecanora sordida_ (_L. glaucoma_), has a vigorous thallus that easily ousts its neighbours. _Rhizocarpon geographicum_, a slow-growing species, is especially liable to be attacked; from the thallus of _L. sordida_ the hyphae in strands push directly into the other lichen in a horizontal direction and split up the tissues, the algae persist unharmed for some time, but eventually they succumb and are used up; the apothecia, though more resistant than the thallus, are also gradually undermined and hoisted up by the new growth, till finally no trace of the original lichen is left. _Lecanora sordida_ is however in turn invaded by _Lecidea insularis_ (_L. intumescens_) which is found forming small orbicular areas on the _Lecanora_ thallus. It kills its host in patches and the dead material mostly drifts away. On any strands that are left _Candellariella vitellina_ generally settles and evidently profits by the dead nutriment. It does not spread to the living thallus. _Lecanora polytropa_ also forms colonies on these vacant patches, with advantage to its growth.