COLOUR OF LICHENS 249 



apothecia of Phialopsis rubra. " Lecanora-red," by which Bachmann desig- 

 nates the purplish colour of the hymenium, is an unfailing character of 

 Lecanora atra; the colouring substance is lodged in the middle lamella of 

 the paraphysis cells; it occurs also in Rhizocarpon geographicum and in Rh. 

 viridiatrum; it becomes more deeply violet with potash. M. C. Knowles^ 

 noted the blue colouring of Rk. geographicum growing in W. Ireland near 

 the sea and she ascribed it to an alkaline reaction. Two more rare pigments, 

 " Sagedia-red " and " Verrucaria-red," are found in species of Verrucaria- 

 ceae. These tinge the calcareous rocks in which the lichens are embedded 

 a beautiful rose-pink. They are scarcely represented in our country. 



5. Brown. A frequent colouring substance, but also presenting several 

 different kinds of pigment which may be arranged in two groups : 



(i) Substances with some characteristic chemical reaction. These 

 are of somewhat rare occurrence: " Bacidia-brown " in the middle lamella 

 of the paraphyses of Bacidia fuscorubella stains a clear yellow with acids 

 or a violet colour with potash ; " Sphaeromphale-brown," which occurs 

 in the perithecia and in the cortex of Staurothele clopismoides, becomes 

 deep olive-green with potash, changing to yellow-brown on the application 

 of sulphuric acid ; " Segestria-brown " in Porina lectissima changes to a 

 beautiful violet colour with sulphuric acid, while " Glomellifera-brown," 

 which is confined to the outer cortical cells of the upper surface of Parmelia 

 glomellifera, becomes blue with nitric and sulphuric acids, but gives no re- 

 action with potash. Rosendahl^ confirmed Bachmann's discovery of this 

 colour and further located it in corresponding cells of Parmelia prolixa and 

 P. locarensis. 



(2) Substances with little or no chemical reaction. There is only 

 one such to be noted: " Parmelia-brown," usually a very dark pigment, which 

 is lodged in the outer membranes of the cells. It becomes a clearer colour 

 with nitric acid, and if the reagent be sufficiently concentrated, some of the 

 pigment is dissolved out. .Some tissues, such as the lower cortex of some 

 Parmeliae, maybe so impregnated and hardened, that nothing short of boiling 

 acid has any effect on the cells; membranes less deeply coloured and changed, 

 such as the cortex of the Gyrophorae, become disintegrated with such drastic 

 treatment. With potash the colour becomes darker, changing from a clear 

 brown to olivaceous-brown or -green, or in some cases, as in a more faintly 

 coloured epithecium, to a dirty-yellow, but the lighter colour produced there 

 is largely due to the swelling up of the underlying tissues to which the potash 

 penetrates readily between the paraphyses. 



" Parmelia-brown " is a colouring substance present in the dark epi- 

 thecium and hypothecium of the fruits of many widely diverse lichens, and 



^ Knowles 1915. ° Rosendahl 1907. 



