INTRODUCTION TO CRYPTOGAMIC BOTANY. 415 



on calcareous jocks. The apothecia are at first closed, but ex- 

 posed in consequence of the dimidiate excipulum splitting in a 

 radiating manner. The nucleus at length falls out, and leaves 

 a little pit in the stroma. Lecanora affinis, esculenta, and 

 their allies have already been spoken of on account of their 

 curious habits, and their value as an article of food. Their 

 gonidia deserve especial notice, because they are contained in 

 distinct asciform cavities amongst the cortical tissue, though 

 resting on the medullary (Fig. 87, c). These species vary from 

 solid tuberiform bodies to fruticulose fascicles. 



453. Tulasne has discovered spermatia in most genera, which 

 differ considerably even in the same genus. The genera are 

 probably all cosmopolitan, except Dirina, which belongs to 

 southern Europe, the regions of the tropics, and south Africa. 

 (We say nothing of the small and obscure genera Gyalecta and 

 Gassicurtia.)* A considerable number of species also occur 

 in all parts of the world. The decidedly foliaceous ParmelicB 

 abound in the cold and temperate regions of both hemispheres, 

 but bear a much smaller ratio to the whole number of species 

 within the tropics. Thus, to speak roughly, the foliaceous 

 species (=Imbricaria and Physcia) are in Europe as 30 : 500, 

 in French Guiana as 5 : 200; i.e., as 1 : 17 in one case, and as 

 1 : 40 La the other ; so that the foliaceous Parmelice are at least 

 twice as numerous proportionally in Europe as in tropical 

 America. The section called Psora by Fries, in his Lich. Eur., 

 is most plentiful in the temperate regions of the south. New 

 Zealand contains, perhaps, twice as many species as we have in 

 Britain, out of a Lichenological Flora, comprising at present 

 about half the number of our own species, but which probably 

 may in reahty exceed it. 



* By Oassicurtia is here meant the genus published under that name 

 in Linnssa. The Oassicourtia alluded to at page 378, as having scarlet 

 sporidia, and so spelt in Orbigny's Dictionary, is probably an anamor- 

 phosis of some Lichen, belonging to the same category as Eypochnus. 

 It is now called by F^e Cystodium, and regarded as a Fungus, but this 

 is evidently incorrect. The scarlet bodies are not sporidia, but granu- 

 lar bodies similar to those which occur in Stegoholus, and other genera. 

 I can, however, only speak of them from report, as I have seen no 

 specimen. 



