( 44 ) 
accommodated to the nomenclature of this book of what is said. The 
author had already (I. c. 3, p. 146) delineated the ‘unbroken series’ of 
Parmeliaceous types, which, connected with the Usneei through the 
ascendant conditions of Theloschistes and Physcia, continues to develope 
itself in the foliaceous forms of these genera, and Parmelia, and reaches 
the summit of such development in Sticta and Nephroma. From these 
last ‘branch off’ (differenced by the disappearance of the cortical layer 
on the under side of the thallus) Peltigera, and Solorina. And, related 
more closely to Sticta by the continuousness (not, however, without 
important exceptions) of its cortical layer, next follows Pannaria, con- 
stituting with Lecothecium and Pterygium but a single family. From 
Lecothecium, ete., ‘the transition to the Collemacee, is, whether we regard 
the medullary tissue or the gonidia, plainly a gradual one.’ And, in like 
manner, the Collemace, for their part, connect themselves, immediately, 
with the just referred to representatives of the Pannaria group. And 
the author continues, still more particularly, in introducing his discussion 
of the structure of Pannaria, as follows (p. 190)— The few species of 
this remarkable genus mediate the transition of the so-called heteromer- 
ous Lichens into the homeomerous. While some (P. plumbea, hypnorum 
etc.,) remind us in habit as well as anatomical characters of the Par- 
meliacea, others (P. rubiginosa and tryptophylla) display a decided rela- 
tionship to the Collemacee ; without at the same time any room being left 
to doubt that all are alike referable to the same natural group. In 
P. rubiginosa and tryptophylla, and sometimes also in P. microphylla, the 
gonidia possess, namely, thickened, gelatinous membranes, which often 
completely fill up the interspaces of the filamentous tissue, and appear 
even not seldom dissolved into a homogeneous pulp; in which, as in the 
Collemacee, filaments and gonidia are imbedded. It follows from this, 
he goes on finally to say, that the whole gonidium-bearing, or much the 
larger part of the thallus, in these instances, assumes the character of a 
gelatinous tissue, not essentially differenced from that of typical Colle- 
macce ; and that only the smaller part, reduced sometimes, here and 
there, almost to nothing, retains the normal features of the heteromerous 
frond. * For further illustrations of the pregnant fact just stated, 
1“ Die grossere Zahl der aiufgefiihrten Gattungen ldsst sich in eine ununter- 
brochene Reihe bringen, in weleher jede folgende sich unyezwungen an die vor- 
hergehenden anschliesst. Geht man von Anaptychia aus, welche den Uebergang 
zu den strauchartigen Formen vermittelt, so folgen nacheinander die iibrigen 
Gattungen der Parmelicen ; Parmelia, Physcia, Imbricaria. -4n diese reihen sich 
durch Vermitthing von Stieta herbacea, pallida, dissceta und der tibrigen Arten, 
dic zu den Nylander'schen Gattungen Ricasolia und Sticta gehdren, die Genera 
Sticta und Nephroma, beide zum Theil mit typisch blaugriinen Gonidien und unter 
sich vollkommen iibereinstimmend. Folgen nun, um die Reihe der allseitig um- 
rindeten Flechten nicht zu unterbrechen, zundchst die Pannarien, an welche dic 
tibrigen als Pannariaceen aufgefihrten Gattungen sich anschliessen. Zwischen 
