The presence of these coloured substances enables the cell-wall to resist chemical reactions induced by the harmful influences of the atmosphere or of the substratum. The darker the cell-wall and the more abundant the pigment, the less easily is the plant injured either by acids or alkalies. The coloured tips of the paraphyses thus give much needed protection to the long lived sporiferous asci, and the dark thalline tissues prevent premature rotting and decay. _d._ ENUMERATION OF AMORPHOUS PIGMENTS: =1. Green.= Bachmann found several different green pigments: “Lecidea-green,” colouring red with nitric acid, is the dark blue-green or olive-green (smaragdine) of the paraphyses of many apothecia in the Lecideaceae, and may vary to a lighter blue; it appears almost black in thalline cells[889]. “Aspicilia-green” occurs in the thalline margin and sometimes in the epithecium of the fruits of species of _Aspicilia_; it becomes a brighter green on the application of nitric acid. “Bacidia-green,” also a rare pigment, becomes violet with the same acid; it is found in the epithecium of _Bacidia muscorum_ and _Bacidia acclinis_ (Lecideaceae). “Thalloidima-green” in the apothecia of some species of _Biatorina_ is changed to a dirty-red by nitric acid and to violet by potash. Still another termed “rhizoid-green” gives the dark greenish colour to the rhizoids of _Physcia pulverulenta_ and _P. aipolia_ and to the spores of some species of _Physcia_ and _Rhizocarpon_. It becomes more olive-green with potash. =2. Blue.= A very rare colour in lichens, so far found in only a few species, _Biatora_ (_Lecidea_) _atrofusca_, _Lecidea sanguinaria_ and _Aspicilia flavida_ f. _coerulescens_. It forms a layer of amorphous granules embedded in the outer wall of the paraphyses, becoming more dense towards the epithecium. A few granules are also present in the hymenium. =3. Violet.= “Arthonia-violet” as it is called by Bachmann is a constituent of the tissues of _Arthonia gregaria_, occurring in minute masses always near the cortical cells; it is distinct from the bright cinnabarine granules present in every part of the thallus.