150 HARSHBERGER : PHYTO-GEOGRAPHIC SKETCH 
turbed, sapling hemlocks, beeches and red maples are present ready 
to replace the dominant trees when they have succumbed to the 
wind. On the floor of the forest in places Lycopodium lucidulum 
Michx. forms an association (Lycopodium association). The laurel, 
Kalmia latifolia L., occurs in the drier soils and forms a thicket 
(Kalmia association). Mitchella repens L. carpets the ground (AMit- 
chella association) and Viola rotundifolia Michx. is a character- 
plant with which grows Peramium pubescens (Willd.) MacM., Czuna 
latifolia (Trev.) Griseb., Hieracium paniculatum L., and in late 
summer Aster divaricatus L. In many places, the hemlock, 7suga 
Canadensis, forms an element in the mixed-deciduous-forest 
formation. When such is the case, it is found in isolated patches 
usually of a few trees near the water-courses on steep hillsides. It 
forms then an association (7swga association) and with Lycopodium 
lucidulum are found three other species, viz., Lycopodium annotinum 
L., L. clavatum L., and L. obscurum L. (L. dendroideum Michx.), 
which grow near ihe hemlocks. Two alternative hypotheses may 
be adduced for this. Either an original hemlock forest has been 
replaced by a deciduous one, or occasional hemlock trees have 
been under certain edaphic conditions developed amidst the com- 
ponent species of the deciduous forest. ; 
SERPENTINE-BARREN TREELESS FORMATION.—The details con- 
cerning this formation will not be given here, as an account has 
been given elsewhere of the character of the vegetation of the ser- 
pentine barrens.* The herbs found upon the broken-down ser- 
pentine rock are Phlox subulata L. (Phlox association), 77 yifolium 
aureum L. (T. agrarium L.), Pteridium aquilinum (L.) Karst. 
(Pteris aquilina L.), Verbascum Blattaria L., Panicum latifolium L., 
Potentilla Canadensis L., Cerastium oblongifolium Torr. (C erastium 
association), Sezecio Balsamitae Muhl. (Senecio aureus Balsamitae 
Torr. & Gray), Castilleta coccinea (L.) Spreng., Arenaria stricta 
Michx., Zalinum teretifolium Pursh, [rophorus glaucus (L.) Nash 
(Setaria glauca Beauv.), Aster ericoides depauperatus Porter, P oly- 
gonum tenue Michx., Lespedeza Virginica (L.) Britton, Andropogon 
scoparius Michx., Solidaga puberula Nutt., Eupatorium aronaticum 
L., Panicum dichotomum L., Koellia flexuosa (Walt.) MacM. 
Harshberger, J. W. The flora of the serpentine barrens of southeast Pennsyl- 
ania. Science, II. 18: 339-343. 11 S 1903. 
