278 BOTANICAL GAZETTE foctoties 
being by far the most extensive and the best one for such an investi- 
gation. For a comparison of the effect of north and south exposures, 
we may select a smaller riprap, consisting of a single extension, and 
lying directly across the track from the one on which occurs the society 
studied above. Indeed, the plants of the single extension on the 
south side of the track might perhaps be considered a portion of the 
society on the north side, but it was thought a separate consideration 
of them would better show the marked difference in character of the 
flora. The single extension is of about the same length and width 
as each one of the four on the north side of the track and makes 
about the same angle. The land to the south of the track is a low 
meadow with conditions distinctly less moist than in the swamp 
the north. Yet more pronounced is the drying effect of southward 
exposure, and altogether we have distinctly more xerophytic condi- 
tions on this single riprap extension on the south side of the track. 
Plainly less shade is to be found on the southward exposed extension, 
and as a result of drier conditions the riprap blocks are much less 
disintegrated than those on the north side. A discussion of the spe 
cies of lichens on the riprap south of the railroad track will demon- 
strate a remarkably nice adjustment between lichen structures and 
ecologic conditions. The species are as follows: 
Acarospora_xanthophana (Nyl.) Fink, scarcely infrequent; A. cervina huxale 
(Schrad.) Fink, frequent; A. cervina cinereoalba Fink, frequent; Biatora mynioca 
poides (Fr.) Tuck., rare; Buellia myriocarpa (DC.) Mudd, frequent; Verrucan® 
fuscella Fr., frequent; Lecanora muralis Ach., infrequent; L. subfusca ) 
Ach., rare; Placodium cerinum (Ehrh.) Naeg. & Hepp, scarcely infrequent; 
P. vitellinum (Ehrh.) Naeg. & Hepp, rare; Parmelia conspersa (Ehrh.) Ach., one? 
seen in a somewhat protected spot; Cladonia fimbriata coniocraea (Fit.) Wain, 
once seen in a protected and shaded spot. cal 
Besides the above, the Amphiloma-like plant is sparingly f es 
on this southward-exposed extension, occurring in shaded spots 
especially toward the base, where it is sometimes in more © 
cee ° : . ith those of the 
positions. Comparing the lichens of the list above WI mere 
list for the northward-exposed riprap across the track, we ‘ifierest 
the general structure of the plants in the two societies 1S bec oa te 
Biatora myriocarpoides, abundant on the north side, 1s a os 
south side; and the Acarosporas, each once seen on the no eee: 
all frequent on the south side. In the more xerophytic © 
