124 THE SPORES OF LICHENS. 
spore-cases. It is to be observed, however, that the typi- 
eally colored spore is often, as Professor Tuckerman ex- 
presses it, decolorate. Thus the spores of Buellia petrea, 
are often, and always, so far as I have observed, in a form 
which occurs on rails, colorless, and frequently only 2-blast- 
ish. Similar conditions also occur of Rinodina sophodes and 
R. ascociseana. Pertusaria is another genus in which the 
spores should probably be considered as typically colored. 
They are usually of a yellowish tinge, and in one specimen 
of P. leioplaca they were of a rich golden brown. There 
are many genera in which species with spores belonging to 
the typically colored series, have spores always, so far as 
observed, colorless, or “decolorate.” In the genera of all 
the great families of lichens will be found spores corres- 
ponding to these various types; and a table might be con- 
structed, showing the analogies throughout. But into the 
subject of lichen classification it is not my purpose here to 
enter. 
Our illustrations in the preceding number of the Natu- 
RALIST show the different types of spores as thus distin- 
guished; those of T. parietina being polar-bilocular, those 
of Biatora rubella, acicular, and those of Buellia petrea, 
muriform. The adoption of this idea will certainly intro- 
duce an order and clearness into lichenology which it has 
hitherto lacked, and will do away with a host of genera of 
the German and Italian writers, which serve only to en- 
cumber the books and to embarrass and confuse the student. 
There are perhaps some exceptions, as Professor Tuckerman 
admits, in regard to Gyalecta, and as is perhaps the case 
also with Arthonia. But these may disappear with further 
knowledge, and we have to thank the Professor for an idea 
which greatly simplifies a difficult study, and whose advan- 
tages, as he justly remarks, far outweigh its difficulties. He 
has promised a further discussion of the subject in his forth- 
coming work on the Genera of North American Lichens. 
