PHILOSOPHICAL SOCIETY OF WASHINGTON. 77 



ing wild torrents and dashing cascades. Here the flora, thongh 

 less rich and varied, is also characteristic and interesting, and em- 

 braces, among other rare things, Rhododendron maximum, Iris 

 crestata, Scutellaria saxatilis, Pycnanthemum Torreyi, Solidago rupes- 

 tris and S. virga-aurea, var. humilis. On the Maryland side and a 

 mile above the uppermost point thus far mentioned, is the Cabin 

 John run, which the botanist celebrates more for its walking fern 

 (Camptosorus rhizophyllus) than for the world-renowned arch that 

 spans it. 



The next most prolific source of interesting plants is the region 

 of the Great Falls. The collecting grounds begin a mile or more 

 below at Broad Water. On both sides of the canal the country is 

 excellent, rocky and wooded, with stagnant pools and sandy hillocks. 

 On these rocks grow Sedum telephoides and near Sandy Landing 

 are found Vitis vulpina, Arabis patens, A. hirsuta and Triosteum an- 

 gustifolium. In the pools have been found Carex decomposita, Pot- 

 amogeton hybridus and P. pauciflorus, while on a rocky headland a 

 large "water-pocket" has yielded my only specimen of the white 

 water lily (Nymphoza odorata). Crataegus parvifolia, Rumex verticil- 

 latus Steironema lanceolatum, and last but not least, Nasturium la- 

 custre, have also rewarded my researches in this singular and rather 

 weird region. 



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

 around the Falls has proved very fertile in botanical trophies. 

 Polygala ambigua is found near the boat landing, while by climb- 

 ing the cliffs below this point the native of more northern climes 

 may gaze once more upon his familiar Hemlock Spruce, Tsuga 

 Canadensis. Difficult Run, a mile farther down, though indeed 

 difficult of approach, repays the effort with Podostemon ceratophyl- 

 lus, Smilacina stellata, Potamogeton Claytonii, and numerous other 

 herbal treasures. 



3. The Lower Potomac Region. 



Passing next to the lower Potomac, the localities of special in- 

 terest are, 1. Custis Spring, opposite the Arlington estate, with the 

 extensive marsh below, where Sagittaria pusilla, Discopleura capil- 

 lacea, Cyperus erythrorhizus, 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 others, Scrophularia nodosa, 



