40 LINDSAY, ON ABROTHALLUS, 



These peculiar deformities appear to arise as pustules of 

 the thallus, which gradually hecome distended and inflated^ 

 till they assume a bladder-like form. At the same time^ their 

 base sometimes becomes altered into a narrow peduncle^ 

 apparently by a process of contraction in the surrounding 

 tissues, and a pyriform or globular bulla is produced. By 

 continued contraction of the base of adhesion the mass may 

 become free; the peduncle may disappear, and a regularly 

 globular form be produced. In such a state these bladder-like 

 bodies of extreme lightness would readily be carried great 

 distances by the wind, and might accumulate in particular 

 localities. This is doubtless Schserer's var. bullata of C.glauca, 

 of which he says C^Enum. Crit. Licli. Europ./ p. 13, 1850) : 

 '^Tlialli lobulis extremis in capitida inflata transformatis.^^ 

 These pustules or bladder-like dilatations must be regarded 

 as morbid conditions of the thallus, produced by the growth 

 of the parasites. They are analogous to the blisters caused 

 on the leaves, and excrescences from the bark or stems of 

 various of the higher plants produced by the attacks of 

 insects. But it does not appear to me that the anamorphoses 

 of the thallus of P. saxatilis, on which the Abrothalli grow, 

 can be placed in the same category. They are neither dila- 

 tations of, nor excrescences from, the parent thallus, but 

 distinct and superimposed, sometimes easily detachable, 

 growths. I think, therefore, that Korber has taken an 

 erroneous and limited view of the subject when he observes: 

 "Die stellen des Imbricarien- imd Cetrarien-lagers, 

 welche von diesem Parasiten ii berwii chert werden, bilden 

 eigenthlimliche bauschige Anschwellungen, welche das durch 

 den Schmarotzer bedingte Kr'ankeln der Mutterpflanze 

 deutlich verrathen, friiher jedoch als eigne Lager dem Para- 

 siten falschlich zugeschrieben >^airden (p. 216) ; (speaking 

 of P. saxatilis, p. 73) : auf den eignen Lager eigenthiimliche 

 kleinlappige, krankhaft aussehende und mit dem parasi- 

 tischen Abrothallus Bertianus besetzte Polster bildend ; (and 

 of P. caperata) : des Lager der Imbricaria caperata Avird 

 von diesem Parasiten {A. niicrospernms) weniger krankhaft 

 verandert" (p. 216.) His error probably arises from his not 

 having carefully studied the origin and development of these 

 anamorphoses in any considerable number of specimens. In the 

 Bracmar district I have not unfrequently met with globular 

 dilatations or excrescences of the thallus oi Lecanora tartarea, 

 L. ijareUa, L. ventosa, and other lichens, unassociated witli 

 any parasitic growths. Nor have I ever seen such dilatations 

 or excrescences in P. saxatilis, on whose normal lacinife, as 

 I have already stated, the Abrothalli sometimes occur. 



