12 
Cape Ann is the southern limit of the little Sagina no- 
dosa, and there also is found Potentilla tridentata, familiar 
at the Isle of Shoals and on Mt. Washington. Essex 
County seems also to be the southern limit, for this 
region, of Pinus resinosa (Red Pine), Abies nigra (Black 
Spruce), Vaccinium Vitis-Idea, Viola rotundifolia, etc., 
as it is the northern limit of Cupressus thyoides (White 
Cedar), Quercus prinoides (Chinquapin Oak), Polygonum 
Caryi, Draba Caroliniana, Lygodium palmatum (Climbing 
Fern), and others. At Boxford is what has proved thus 
far to be the only New England station for Salix candida, 
and another bog willow, Salix myrtilloides, is occasionally 
met with. At Andover.a locality for Calamagrostis Pick- 
eringii was discovered in the summer of 1879 ; this species 
has only been known before at the White Mountains. 
Among the sedges and grasses, plants too frequently neg- 
lected will be found, many not heretofore supposed to grow 
in the county, and a careful comparison of this list with 
our botanies will show that the range of many species has 
been extended. Although much careful work has been 
done-there yet remains much to be accomplished ; for, be- 
sides the few species that may be added to the list of 
flowering plants, there are many species of lichens and 
mosses not thus far collected, and the fungi and fresh- 
water alge are purposely omitted altogether. The phan- 
erogams and vascular cryptogams are quite fully studied, 
and to the Characez and marine alge but comparatively 
few additions may be expected. 
The early settlement of the county renders this a par- 
ticularly favorable region for the observation of introduced 
plants. From the earliest settlement to the present time, 
foreign species have continued to arrive, many of which, 
like the early colonists, came with the evident intention 
of remaining; for, as the genista, barberry, white-weed 
