
G 
PS i? Ge) <olsochty dc doulw enrsah Wea 
uon, which De Notaris, Leighton, Massalongo, anc 
Koerber have so, sincerely cultivated; and a new con- 
tent was added td the conception of species. These 
groups of individuals derive all their yalue from their 
ideal centres, from the idea, which they more or less 
imperfectly exhibit ; and every advancing approxima- 
tion to completeness in our apprehension of this idea is 
most obviously important, and may be expected to be 
felt throughout the System. How far, and in what 
manner, the present writer's studies incline him to. ap- 
preciate the sporal phenomena of Lichens, will be seen 
from what follows. (*) 
I conceive then, that while less weight than has been | 
often assumed should be given to spore-differences of a 
merely gradal character, or such others as depend only 
upon mensuration, more than has sometimes been al- 
lowed should be yielded to those that seem to be typi- 
cal.{, Analysis appears to me to indicate two well-de- 
fined kinds of lichen-spores, complemented in the high- 
est tribe only by a well-defined intermediate one. In 
one of these (typically colourless) the originally simple 
spore, passing through a series of modifications, always 
(*)All consideration of the notion of ‘species’ is embarassed 
by the different and uncertain values which the word is used to 
express. We must distinguish in order to combine. And so 
short is life, that a generation may be employed in separating, 
what it shall fall to another to bring together again; and yet 
the whole honest concern of both have been the determination of 
‘species.’ Large views are only possible as the results of much 
abgleelie work, either of successive enquirers, or in nature, 
or is it always possible to avoid the construction of ‘species’ 
from material which wre must be well aware is inadequate; such 
species being in fact parts of quantities, the real extent of which 
is unknown éo wus. 
({)The question here touched upon will be considered more at 
large in a work upon the Genera of North American Lichens, 
now 1n preparation 
