24 FLORA OF WASHINGTON AND VICINITY. 



On tlie opposite side of the river the site of the ancient canal around 

 the falls has proved very fertile in botanical trophies. Polygala amhigua 

 is found near the boat-landiug, while by climbing the cliffs below this 

 jjoint the native of more northern climes may gaze once more upon his 

 familiar hemlock sj^ruce {Tstiga Canadensis). Difficult Run, a mile 

 farther down, though indeed difficult of approach, repays the effort 

 with Podostemon ceratophyllns, SmUacina stellata, Fotamogeton Claytoniiy 

 and numerous other herbal treasures. 



3. The Lower Potomac Region. 



Passing next to the Lower Potomac, the localities of special interest 

 are : 1. Custis Spring, opposite the Arlington estate, with the extensive 

 marsh below, where Sagittaria pusilla, Discopleura capillacea, Gyperus 

 erythrorhizos, and other rare species are alone known to grow. 2. The 

 point and bay below Jackson City, known as Roach's Run, where are found, 

 among other good things, Scrophularia nodosa, Tripsacum dactyloides, 

 and Pycnanthemum lanceolatum. 3. Four Mile Run, halfway to Alexan- 

 dria, not yet sufficiently explored, including the vicinity of Fort Scott, to 

 the northwest, where Clematis ochroleuca and Asclepias quadrifolia may 

 be collected ; and, 4. Hunting Creek, a large estuary below Alexandria, 

 including Cameron Run, the stream which debouches into it with its 

 tributaries, Back Lick Run and Holmes Run, which unite to form it. 

 Here have been found at various points Clematis ochroleuca, Gonolohus 

 hirsutus, Itea Virginica, Geranium columhinum, Micranthemum Nuttalliij 

 Habenaria virescens, Quercus macrocarpa, Carex gracillima, Geum stric- 

 tum, Galium asprellum, and very many other rare plants. 



On the left bank of the Lower Potomac the chief locality of interest 



is a large wooded area below the Government Hospital for the Insane. 



This has proved a rich hunting ground I'or the botanist, and has yielded 



Carex pallescens, C. ietanica, var. Woodii, GonoloMts hirsutus, Silene Ar- 



meria, Parietaria Pennsylvanica, Myosotis arvensis, Scutellaria nervosa, 



&c, Asplenium angustifolium is known only at Marshall Hall, where it 



has been collected by Mr. O. M. Bryan, while opposite Fort Foote Mr. 



Zumbrock has found Myriophyllum spicatum, and opposite Alexandria 



Professor J. H. Comstock and MissH. B. Willets have discovered Plan- 



tago cordata. 



4. The Terra Cotta Region. 



This embraces some low grounds and undulating barrens near the 

 terra cotta works at Terra Cotta Station, on the Metroj)olitan Branch 

 of the Baltimore and Ohio Railroad, three miles iiom the city, and also 



