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structions both the generical validity of the effigurate type of thallus, , 
and also that of each of the several gradations in the typical differentia- | 
tion of the spores; and hence not a few subdivisions of the group, cited 
above. It remains thus, as here taken, a large one; but with that objec- 
tion we are little concerned, provided the genus be also, ene sat 
a natural one. ‘Malo . . . contra characteres, quam affinitatem 
naturalem peccare.’ (Fr. Summ. p. 428.) But is it certain that even the 
sharpest characters (those namely derivable from the spores) should not 
be subordinated to the whole idea of the plant? And, still further, is | 
there nothing justifying a fair presumption that a natural group shall | 
tend to exhibit, within its circuit, the entire differentiation of its spore-, 
type? / These questions have been already above touched upon; and the 
writer’s solution of them will appear as well in the now proposed arrange- 
ments of the present, and other large groups. 
Like the preceding genus, the present, as I understand it, passes then 
by quite imperceptible gradations from the subfoliaceous thalline type 
(sect. Sguamaria, ascending also very rarely into fruticulose conditions, 
sect. Cladodium) into the granulose-crustaceous (sect. Hulecanora) which 
last embraces the great bulk of the species, and exhibits the whole differ- 
entiation of the spores. So far, the apothecia (though not without sig- 
nificant anticipations of possible variation) are for the most part regular : 
but this does not continue; and the slight indications of an urceolate 
depression of the fruit observable in Placodium, are expanded here into 
a group (not without effigurate and even fruticulose forms) of well- 
marked lichens (sect. Aspicilia) which paves the way for the extreme, 
variously aberrant, and polysporous section, Acarospora. The distinc- 
tion of the higher modifications of thallus (in sect. Sguamaria and Clado- 
dium) from the granulose, is notwithstanding, from our point of view, 
scarcely a valid one; being determined mainly by the relatively consider- 
able number of higher forms: and the genus may as easily be regarded as 
constituting a single large group — Eulecanora sensu lat.— supplemented 
by two smaller ones. 
The already observed nisus of the crustaceous thallus to elevate 
itself to the foliaceous, and even the fruticulose, is repeated, often on a 
larger scale and with greater diversity of modification, in Lecanora ; but 
the fruticulose type is as rare here as in Placodiwm. It is yet 
represented in North America by no less than three lichens, con- 
fined, like the fruticulose species of Placodiwm, to the Pacific coast. 
—L. Bolanderi, Obs. Lich. 1. ¢. 6, p. 266, was discovered on the sand- 
stone rocks of California by the friendly botanist after whom it is named. 
Terete as is the many-branched thallus of this lichen, it certainly sug- 
gests some conditions of the most perfect (monophyllous) state of L. rubina; 
with which, as with the rest of the Sqguamarie, it also agrees in its 
elongated, bowed spermatia. The comparison may remind us of the 
supposed development of the Asiatic L. fruticulosa, Eversm. (the shorter, 
