PEILTUSARIA. 



297 



with a white, mealy powder, or with numerous, small, globu- 

 lar, white soredia. The apothecia are very frequently abor- 

 tive and sorediiferous, the soredia being then usually scat- 

 tered, large, distinctly circumscribed, globular, flattened or 

 scutellate. We have met with all these forms — frequently 

 combined also with isidioid conditions (E. B. 1511) — on 

 trees in the neighbourhood of Perth, especially on the ash, 

 towards the base of its trunk or on its exposed roots. The 

 variolarioid states of this Lichen include several familiar 

 species of the old genus Variolaria (E. B. 1 713 and 1714). 

 They are chiefly remarkable for the quantity of oxalate of 

 lime which they contain ; so much indeed, that they have 

 been used in Erance as a source of oxalic acid. Hence some 

 varieties taste intenselv bitter: and hence also the foundation 

 of their use as a febrifuge in intermittents. Under the mi- 

 croscope we have found large quantities of octahedral crys- 

 tals, apparently of oxalate of lime, in some foreign variola- 

 rioid varieties of P. communis (the Variolaria amara and V. 

 faginea of older writers), but not so abundantly as in Urceo- 

 laria scruposa. Braconnot found 29 per cent, of oxalic acid 

 in combination with 18 of lime in V. faginea. The thecae 

 of P. communis are very large and strong ; they are two- 

 spored, thick-walled, linear or ribbon-shaped and much elon- 



