248 PHYSIOLOGY 



of the pycnidia are also coloured in some forms; more frequently the cells 

 round the opening pore are more or less brown. 



The presence of these coloured substances enables the celUwall 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 

 ma)- vary to a lighter blue; it appears almost black in thalline cells^ 

 " Aspicilia-green " occurs in the thalline margin and sometimes in the 

 epithecium of the fruits of species oi 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 o{ Bacidia 

 niuscorum 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 oi 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 {Lecided) atrofusca, Lecidea sanguinaria and Aspicilia flavida i. 

 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 oi 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. 



4. Red. Several different kinds of red have been distinguished: "Ur- 

 ceolaria-red," visible as an interrupted layer on the upper side of the medulla 

 in the thallus of Diploschistes ocellatus, a continental species with a massive, 

 crustaceous, whitish thallus that shows a faint rose tinge when wetted. 

 " Phialopsis-red " is confined to the epithecium of the brightly coloured 



' A similar reaction with nitric acid is produced on the blue hypothalline hyphae of Placynthium 

 nigrum. 



