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POPULAR HISTORY OF LICHENS. 



A peculiar, common, and extensively diffused family, at- 

 taining its maximum development in the Tropics, and de- 

 creasing in numerical distribution towards the Poles ; in 

 Lapland only one species exists. Their habitat is usually 

 the smooth bark of forest-trees, but some species are saxico- 

 loas. From their minuteness and protean character they are 

 a difficult family to study; but Leighton has lately done 

 much towards the deciphering of these hieroglyphics of Na- 

 ture, — as Layard and Rawlinson have discovered the signi- 

 fication of the graven characters on the stones of Nineveh, 

 — and has produced a valuable monograph, which is the 

 basis of the characters of the genera and species as here 

 given. * The Graphidece generally appear destitute of a thal- 

 lus. The lirellse may frequently be said to constitute the 

 plant ; but the dissociated elements of the thallus may usually 

 be discovered expanded in the tissue of the bark on which 

 it grows. The spores of the species and genera vary greatly 

 in character ; but in general they may be characterized as 

 elongated, narrow and polycellular or polyseptate. They are 

 frequently linear, fusiform, oblong or clavate, margined, 

 containing rounded or irregular cellules, which are soine- 



* We do not however express an unqualified approval of Leighton's classi- 

 fication ; for we cannot help thinking that he has divided, or split up, the 

 Graphidece to an unnecessary extent. 



