158 College of Forestry 
shrubs as indicators of acid conditions (whatever that may 
mean). The tendency toward dominance of heath-shrubs in 
both bogs and in sand barrens is certainly noteworthy, but 
it should be noted that on the whole, species of Hricaceae 
dominate in bogs while Vacciniaceae dominate in sand bar- 
rens although we found Chamaedaphne (leather leaf) very 
abundant in each and lambkill in both. 
General Survey of Xerophytic Succession in New York. 
Considering the State as a glacially prepared terrain, the 
features which would offer habitats with deficiency of water 
supply — or at least periodic deficiency would be,— 
(1) Bare rock surfaces, polished smooth and left uncov- 
ered by glacial till or denuded of such in post-glacial time. 
This includes glacial stream beds (See Fig. 25); rounded, 
dome-like summits of hills and mountains in the Adiron- 
dack region, Catskills, Highlands of the Hudson, ete.; ver- 
tical rock ledges of mountain sides and of deeply cut stream- 
ways. 
(2) Detached rock fragments accumulating on mountain 
slopes — see Catskills — and smooth rounded boulders de- 
posited by the melting ice — notably in moraines. See Figs. 
21 to 24. 
In (1) and (2), rock fissures and the space between bould- 
ers facilitate the development of vegetation by offering a 
lodgment for finer mineral and organic sediment in which 
plants readily gain a foothold. Seepage may cut a figure on 
mountain sides. Indeed a rocky hillside may thus become ~ 
the location of a hydrophytic sequence —e. g. Sphagnum 
is common in such situations in the Adirondacks. 
(3) Sand deposits; dune sand, delta sand, lake shore sand 
and glacially distributed sands of the Adirondack gneissic 
rocks. The development of heath-shrub is notable here. 
(4) Exposed hills and slopes either where rock lies with 
very thin cover of water retaining till (clay, ete.), or till 
having a large percentage of gravel and sand. 
