LINDSAY, ON ABROTHALLUS. 39 



ash on the roadside hetween Dumfries and Caerlaverock — I 

 have found cubical or octohedral crystals more or less abun- 

 dantly in the thallus, apparently consisting of the carbonate 

 or oxalate of Kme. I have frequently detected crystalline 

 matters of various kinds in the thallus of other lichens. 



The colour of the squamules varies greatly in different 

 habitats and localities. Sometimes they possess a peculiar 

 leaden hue ; such squamules^ whether simple or polyphyl- 

 lous^ are generally sterile^ or they bear pycnides scattered 

 sparingly towards the margins and unassociated with apothecia. 

 In Highland districts especially, the thallus is sometimes 

 of a rusty red or copper colour, depending apparently on the 

 absorption of peroxide of iron. This species of coloration is 

 frequent also in the ordinary thallus of P. saxatilis. At 

 other times the squamules have a light brownish tint on the 

 siu'face ; but the medullary tissue, as exhibited in fissnres of 

 the cortical layer, or in the foveolee left by the falling out of 

 the apothecia of A. Smithii, possesses a brilliant saffron tint, 

 resembling that of the under surface of Solorina crocea. In 

 other cases, the colour approximates that of the thaUus of 

 P. saxatilis, on which the deformations occur. 



The thalli on which A. Smithii is parasitic generally become 

 globose, irregular, gnarled masses, from the evolution of the 

 edges already alluded to, and from the development of suc- 

 cessive and super-imposed crops of new lobes or squamules. 

 This convexity increases ; the base of adhesion becomes nar- 

 rowed by continued curling ; and the globular mass may at 

 length be easily detached from the thallus of P. saxatilis, to 

 which it bears little or no resemblance. The most globular or 

 hypertrophic specimens I have met with have been sterile forms 

 of a leaden hue or light grayish colour, apparently develop- 

 ments of the squamules on which the pycnides of A. Smithii 

 frequently occur alone. A section shows such a mass to consist 

 of a series of irregularly disposed layers of squamules or 

 lobes, sej)arated by alternate strata of a brownish granular 

 matter, the debris of the rhizinae or black fibrils of their 

 under surface. I have never seen these masses free; but, 

 from a consideration of their mode of growth, I have no 

 doubt that they may be ultimately detached by the wind or 

 other agencies, and, continuing to vegetate in the way I have 

 described, may become regularly globular, all trace of the base 

 of adhesion being obliterated. In a specimen oi A. oxysjjorus 

 on Cetraria glauca, from Barmouth, North Wales, for which 

 I am indebted to Mr. Leighton, the parasite grows on pecu- 

 liar bullose dilatations of the extremities of the lacini^, or 

 of some more central portion of the thallus of the Cetraria. 



