FLORA OF WASHINGTON AND VICINITY. 65 



Nasturtium lacustre, Gray. Lake- Cress. 



Only found in one of the numerous pools among the rocks below Great Falls. In 

 flowering time, at the end of June, it presents three kinds of leaves. The pond in 

 which it has been submersed during the spring, and where it has borne only dis- 

 sected leaves, is then dry, and the long stems lie prostrate on the muddy bottom 

 with the whorls of these leaves adherent to them. At the base a rosette of broad, 

 green leaves, more or lesslobed orlyrate, springs up, while the upper portion of the 

 stem below the flowers bears small, lanceolate or oblong, entire leaves. 



Nasturtium. Armoracia, Fries. Horse-Radish. 

 Very sparingly escaped. 



Barbarea vulgaris, R. Br. Winter-Cress. 

 Early in April. 



Barbarea prcecox, R. Br. Early Winter-Cress. Scurvy-Grass. 



First week in April. Rosettes of radical leaves develoj) during the winter. 



tArabis lyrata, L. Rock-Cress. 



On much exposed rocks. The radical leaves can only be obtained very early in 

 April or even in March. April. 



Arabis dentata, Torr. and Gray. 



High Island and islands above; also South shore of the Potomac. April. 

 Arabis patens, Snlliv. 



Sandy Landing. Rare. Middle to end of April; pods persistent until August. 

 Arabis hirsuta, Scop. 



Near Sandy Landing. Mr. C. S. Sheldon, May 22, 1881; then with young fruit, 

 t Arabis laevigata, Poir. Tower-Mustard. 



April. 

 tArabis Canadensis, L. Sickle-Pod. 



Third week in May; fruit in July, 

 t Cardamine rhomboidea, DC. Spring-Cress. 



Early in April, 

 t Cardamine hirsuta, L. Bitter Cress. 



Always wholly glabrous. First week in April. Autumnal flowers collected Octo- 

 ber 3, 1880. 



t Cardamine hirsuta, L., var. sylvatica, Gray. 



A much smaller plant than the last, and apparently distinct. Pleasantly flavored. 

 First week in April. 



tDentaria heterophylla, Nutt. Diverse-leaved Toothwort. 



Virginia shore of the Potomac, above Georgetown. Middle of March to middle 

 of April. 



tDentaria laciniata, Muhl. Cut-leaved Toothwort. 



Middle of March to middle of April. When this species and the last are found 

 growing together there is a diflereuce of a week in their flowering time, this being 

 the earlier. 



Draba ramosissima, Desv. Branching Whitlow-Grass. 



Rocks at Harper's Ferry ; may be looked for nearer. May 30, 1873. 

 Bull. Nat. Mus. No. 22 5 



