(87) 
quent study, and the point of departure of Flotow (1. c.) Koerber (Syst. 
lc. Parerg.) and Nylander. 
But the advance of knowledge, since Fries wrote, leaves the Hucol- 
lemei by no means where they were when he reconstructed the group. 
Omphalaria, most clearly touching Collema (as seen in the comparison of 
C. chalazanum, &c., with O. cyathodes) on the one hand, brings it next 
into no questionable relation with the once distant Synalissa, on the 
other. Indeed this latter relationship is fully implied in Fries’s final 
reference (Summ. Veg. Scand., suppl.) of Omphalaria phyllisca (Endo- 
carpon, Wahl., Fr. L. #.) to Synalissa. Nor has the connection of the 
assemblage now immediately before us proved in fact much less intimate 
with Leptogium. Here however the for the most part sufficiently strik- 
ing difference in habit effectively intervenes; and has proved enough to 
countervail even Anzi’s demonstration of a cellular cortical layer in Col- 
lema aggregatum. And the parallel spore-history of these two groups, 
(Collema and Leptogium) as here taken, looks perhaps in the same direc- 
tion; that is to their continued separation. 
This spore-history is especially interesting; and cannot be passed 
without some brief consideration. In a general view of the spores of 
‘true Lichens,’ as these are distinguished by most authors from Collema- 
ceous Lichens, it will perhaps be admitted to be easy to reach the infer- 
ence already presented by the writer in print (Lich. Calif. p. 6) that all 
known modifications of spore-structure, to whatever extent distinguish- 
able among themselves, are yet reducible to variations of but two clearly 
defined types; and that it is less feasible at present to subsume them 
under one. Led by such instances as Parmelia, Lecanora, Biatora, and 
Lecidea, on the one hand, and Physcia, Rinodina, Heterothecium, and 
Buellia, on the other,—by so large and important a proportion of the 
class, —we have seemed then to discern two series (1. c. p. 9) and really 
to be able, for the most part, to distinguish these series, notwithstanding 
decoloration and other exceptions, in a manner as satisfactory as were at all 
to be expected. Much of the argument of the present book proceeds 
from this assumption, and will now be left ‘for what it shall prove to be 
worth’ (L. c. p. 10) satisfied as I am that the results reached are not with- 
out value. But the difficulties remain. It is possible, I believe, by a 
sufficiently extensive investigation of the whole spore-development of 
such natural groups as Thelotrema and Pyrenula, as here understood, 
and a careful appreciation of the varied details, to explain most apparent 
anomalies as decolorate exhibitions of stages of evolution of the muri- 
form or (normally) coloured spore ; and these large and analogous genera, 
the extraordinary exuberance of variation in the apothecia of the one of 
which exhibits so curious a contrast with the poverty of the other, appear 
thus to be more readily interpretable than some smaller ones. This is 
not however at present the case with Gyalecta, Anz.; as evidenced espe- 
cially in this writer’s striking comparison of his G. acicularis (Catal. 
