1857.] BOTANY OF PERTH. 269 



differ greatly in size and in the degree and mode of division ; its 

 rudimentary or young state appears to be one species of the old 

 genus Lepra or Lepraria, which is now found to be made up of 

 rudimentary, sterile, or abortive forms of other species and ge- 

 nera. An examination of the sorediiferous degenerations of the 

 thallus of Lichens, and of the varieties producible in the cha- 

 racters of the thallus, by changes in external circumstances, has 

 led to the expulsion from our modern systems of classification of 

 the genera Lepra or Lepraria, Spiloma, Isidium, and Variolaria, 

 all of which consist of abnormal or young states of better-esta- 

 blished and more familiar genera or species. 



Lecanora saxicola and L. coarctata are common and abun- 

 dantly fertile on the rocks of the summit of Kinnoull Hill. L. 

 atra is abundant on walls and rocks throughout the district, 

 sometimes forming a complete coating of the tops of walls, as 

 about Invergowrie. It exists also in variolarioid, or sterile and 

 abortive states. Lignicolous and sasicolous forms of L. suhfusca 

 abound everywhere. There is great variety in the form and 

 colour of the apothecia, which are sometimes black, in which 

 case this species cannot be easily distinguished from L. atra. 

 In the latter Lichen however the apothecia are black, ab itiitio, 

 while in the former they only become so with advancing age. 

 Saxicolous and lignicolous forms of L. pallescens, var. parella, 

 likewise are abundant, both in the fertile and in the isidioid and 

 variolarioid conditions. Isidioid forms occur chiefly on rocks 

 and stones ; such forms of this and other Lecanoras — as L. ri- 

 mosa — constitute the chief species of the old genus Isidium, and 

 are valuable as tinctorial Lichens. Variolarioid states generally 

 occur on trees, where they are often associated with similar con- 

 ditions of Pertusaria communis : I have noticed them chiefly in 

 winter, when the trunks of many of the larger forest-trees in the 

 woods of Kinnoull and Kinfauns seem covered with species of 

 the old genus Variolaria. L. tartarea occurs, but seldom in 

 fructification, on trap-rocks in one of the transverse ravines or 

 valleys of the Sidlaws, behind Kinfauns, associated with L. h<2- 

 matomma, L. pallescens, var. parella, and Urceolaria scruposa, 

 and also, along with L. ventosa, on a huge gneissic boulder on 

 the Strathmore Hill road, a few miles beyond Bonhard. The 

 occurrence of this, with other alpine or subalpine Lichens, at an 

 elevation so moderate, and on a boulder of such mineralogical 



