(88 ) 
Sondr. p. 62. Lich. Langob. n. 81) with the at once similar and yet dis- 
similar G. cupularis. And Collema affords a still better example of the 
same sort. We have here, in one series of, in the last analysis, mutually 
explanatory forms, all the most important modifications of spore-structure 
known to Lichens. What is evidently a decolorate example of the muri- 
form spore is traceable backward to regularly quadrilocular — bilocular— 
simple conditions, which then, again, narrowing and lengthening, pass 
finally into the perfect acicular type. There is no question of the 
extremes of evolution reached, or of the completed mediation of these 
extremes, within the limits of a single process of differentiation, and of a 
single group. ? 
In attempting next, on the basis of the latest universal résumé, that 
of Nylander (Syn.) some reckoning of the number of probable species of 
Collema known, it appears desirable to view the group apart from the dis- 
crepant forms, provisionally only, for the most part, associated with it; 
and, in this view, to exclude therefore all plainly crustaceous, as certainly 
doubtful, species; all forms which are associable, by their attachment, 
with Omphalaria; and, as well, the confessedly ambiguous C. byrseum 
(Afzel) (Physma, Mass.) and C. opulentwm (Mont.) (Homothecium, Mass.). 
As to the remainder there is no controversy, beyond what hinges on 
the value of the spore-differences, already immediately above, as elsewhere 
considered; and the always uncertain estimates of what constitutes 
species. Of typical Collema, as thus understood, something over forty 
species have then been reckoned. These are largely northern, and 
especially European; but the number common to America with Europe 
will probably be increased. The number of forms running into or pecu- 
liar to the warmer and intertropical regions of the earth is small; and the 
group contrasts with Leptogium in this respect. Much, we can hardly 
doubt, remains to be discovered, as certainly to be fully determined, here ; 
especially in our calcareous districts. And if the large, long known, and 
important cluster represented by C. pulposum is still so uncertain in 
Europe, as the varying opinions of lichenographers, with regard not only 
to the inner circle of more evidently related forms, but no less to the to 
these strictly akin C. limosum, C. crispum, C. plicatile of authors —not 
to speak of still other more recent discriminations —demonstrate it to be, 
we may well hesitate in positively determining the little we have yet 
learned of the group, in North America. 
We are at once embarrassed, in attempting to arrange our species 
according to the method of this book, by the ambiguity of the spore- 
1 The spores of Collema are commonly defined as colourless; Th. Fries (Lich. 
Arct.) denoting however these organs in several species as ‘Jutcolo-hyaline’ or 
‘luteole, and Mudd (Man. Brit. Lich.) describing them, in nearly half of his 
species, as more or less ‘ pale yellow.’ In about the same proportion of my American 
Collemas, similar indications of colour are often, or more or less observable; or the 
spores at least seen to be brownish, while still included in the thekes. 
