LINDSAY, ON ABROTIIALLUS. 57 



yet fully acquainted. I have never found them on the ordi- 

 nary thallus of the common Parmelia saxatU'is (tlie var. 

 leucochroa of Scluerer's ' Enum. Crit/) ; and I have looked 

 for them in vain on furfuraceous states in a variety of loca- 

 lities. Mr. Leighton mentioned to me recently {in lit.) that 

 he has never found Abrothalli in Shropshire^ though he has 

 frequently looked for them ; and that in Wales they are by 

 no means plentiful. It is very desirable that collectors should 

 direct attention to this subject. 



The apothecia first appear about the centre of a squamide^ 

 where also the oldest and most fully developed specimens are 

 to be found. The tlialli on which A. oxysporus occurs are 

 more frequently simple or polyphyllous squamules^ and tend 

 less to become globose and hypertrophic than those habited 

 by A. Smithii. The yoiing apothecia are punctiform^ black, 

 and scattered : they are frequently very similar to the spermo- 

 gones, fi^om which they can only be distinguished by the 

 absence of an ostiole, and by microscopical examination. In the 

 process of evolution, they more frequently fissure the cortical 

 layer than those of A. Smithii ; the surface of a squamule is 

 sometimes marked by a network of these fissures, which run 

 into, or anastomose with, each other. In the old state the 

 apothecia sometimes become tuljerculiform or maculiform ; 

 their surface is seldom raised much above the level of the 

 slu'rounding cortical tissue, unless Avhen moistm-e is applied. 

 In the latter case the apothecium swells, the siu'face becoming 

 more or less raised or convex. Moisture generally also 

 changes its colour from a black to a light brown, but not 

 invariabl3^ The moistened, brown, swollen apothecium some- 

 times appears as if it Avere a discoid mass of gelatinous con- 

 sistence. I have occasionally observed the apothecia depressed 

 or saccate, as in specimens from the Highland road between 

 Blairgowi'ie and Spittal of Glenshee. Tulasne says the apo- 

 thecia are " punctiformia s. potius discoidea;" the former 

 character appears to apply, however, only to young and 

 undeveloped specimens, and not to normal matiu'e apothecia. 

 Besides the difterent effects of moisture on the apothecia of 

 A. Smithii and A. oxysporus, the former remaining black, 

 the section shoAvs a deeper colour in the former than in the 

 latter — black to the naked eye, but brown under the micro- 

 scope. I have frequently observed sections of the apothecia 

 of ^. Smithii of a purple tint; while those of A. oxysporus 

 have been invariably light brown. Besides the spermogones, 

 the young apothecia are apt to be confounded Avitli the 

 pycnides of A. Smithii, and with certain parasitic fungi, 

 which I have occasionally found interspersed ; but these. 



