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POPULAR HISTORY OF LICHENS. 



everywhere ; it is abundant in woods and on roadside trees 

 and walls. Some varieties are peculiar to certain trees or 

 rocks ; for instance, var. pinastri, a non-granulose, leprose, 

 yellowish or greenish form, grows on the bark of the Pinus 

 sylvestris, the " Scotch fir and var. crenulata, which has 

 small, flattened, subpruinose apothecia, with a tumid crenu- 

 late margin, grows chiefly on calcareous stones. A curious 

 form, having a papillose-ramulose thallus, covers in patches 

 decayed heather or moss in some parts of the Highlands : 

 this was one of the Isidiums of old writers (Isidium ocu- 

 latnm, E. B. 1833), a genus which is now found to con- 

 sist chiefly of isidioid, sterile and abortive forms of various 

 species of Lecanora, — as L. pallescens, L. rimosa, and L, 

 suhfusca. In some young thalli we have observed, under 

 the microscope, abundance of octahedral crystals, probably 

 of oxalate of lime ; but as in the case of acicular crystals in 

 the young thallus of Parmelia jparietina, we have not been 

 able to satisfy ourselves that these do not really belong to 

 the bark on which the Lichens grow. The spores of L. 

 suhfusca are small, oval or ellipsoid, colourless, simple or 

 double- walled, and are in the mature state full of homo- 

 geneous oil. They germinate in the same way as those of 

 Parmelia joarietiua. The spermogones may be observed 



