type in Parmeliacei) a second (typically brown or brownish) in 

 which the simple spore, completing another series of changes, 

 tending rather to distention, and division in more than one 

 direction, exhibits finally the stone-wall-like (muriform) type. (*) 

 Differences such as these appear certainly to be significant ; and 

 to suggest a possible correlation with others, which shall leave 

 no doubt that these types require marked expression in the 

 System. Nor is such expression questioned in the best -devel- 

 oped, foliaceous groups. Nobody now hesitates to distinguish 

 Physcia and Pyxine from Parmelia ; or Solorina from Peltigera ; 

 and the argument from such foliaceous to the analogous crus- 

 taceous genera is impeded perhaps by nothing beside the thai- 

 line inferiority of the latter. But it is seen at once that the 

 case is not the same with the successive steps in the process of 

 differentiation of these types ; and the value of suchgradal (biloc- 

 ular, quadrilocular, plurilocular) distinctions should be clearly 

 inferior. Species which exhibit the ultimate condition of their 

 spore-type, as here taken, exhibit also, ideally at least, or in a 

 sufficiently extended view, the whole of the preceding process 

 of evolution. This is still better observed in larger natural 

 groups, as (exc. excip.) Biatora vernalis, Fr. L. E., expressing, 

 with general congruity of structure, the whole history of the 

 colourless spore. And the step is not a long one from such 

 groups to natural genera ; to the assumption that gradal differ- 

 ences of the same type of spore, displayed by species, or clus- 

 ters of species, within the circuit of what is otherwise a natural 

 genus, shall be an insufficient ground for the breaking up of 



(*) The distinction of the two principal types of spore speaks per- 

 haps for itself; and the history of the acicular type seems tolerably 

 clear. But the author indicated, at the place to be cited below, the 

 difficulties in the spore-characters of Sticta, Gyalecta, and Thelotrcma, 

 as here understood; and, according to Minks (Symb. p. 41), the note of 

 coloration was unduly stretched in including in the second or Coloured 

 Series, the morphologically separate spores of Arthonia, and the Cali- 

 ciacei. 



