















Bi 
‘ 
ne direction, and bis constantly to elongation, 
ford Tenth)" the acieilar ipe. To this is opposed 
(most freq néntly bat not exclusively in the lower tribes, 
nd even possibly “anticipated | ‘by the polar-bilocular 
ub-type i n Parmeliacei) ‘a second, (typically coloured) 
‘fi Sy the simple spore, e; completing & another series of 
changes, tending rather to distention, and to division in 
rn nore than one direction, exhibits finally the muriform 
"Differences such as these may certainly appear to 
e sign ignificant, and to suggest a possible correlation with 
‘others, which shall leave no doubt that these types re- 
quire marked expression in the System. Nor is such 
‘expression questioned i in the case of the best-developed, 
‘foliaceous groups. Nobody now hesitates to distinguish 
i Physcia” and Pyrine from Parmelia, or Solorina from 
Paltigera and the argument from such foliaceous to the 
‘analogous crustaceous genera is impeded perhaps by 
‘nothing beside the thalline inferiority of the latter. 
“But, prima facie, the case is séen to be not the same 
with the successive steps in the process of differentia- 
tion of these Lint and the value of such gradal (biloc- 
jolar, quadrilocular, plurilocular) distinctions should be 
ertainly inferior. Species which exhibit the ultimate 
: “eondition of their spore-type, as here taken, exhibit also, 
: ideally at least, the whole of the preceeding process of 
‘evolution. This is still better seen in larger natural 
groups, as (exe. 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 differences of the same spore- 
type, displayed by species, or clusters of species, within 
the circuit of what is otherwise a natural genus, shall 
be an insufficient ground for the sundering of sucl: 
