90 FLORA OF WASHINGTON AND VICINITY. 



tPolymnia Uvedalia, L. 



September. 



1 Silphium trifoliatum, L. Rosin-Plant. 



July. 



t Chrysogonum Virginianum, L. 



April aud May. Often flowers at the height of 3"="' or 4<=™, and continnes flowering 

 while the stem elongates, after the manner of Saxifraga Virginiensis, q. v. Autum- 

 nal 'flowers observed October 9, 1881. 



t Ambrosia trifida, L. Great Ragweed... 



August, September. 



t Ambrosia trifida, L., var. integrifolia, Gray. 



August, September. 



t Ambrosia artemisiaefolia, L. Roman Wormwood. Hog- weed. Bitter-weed_ 

 Tends to become dioecious, and the fruiting plants crowd out the staminate ones. 

 August, September. 



V 



tXanthium strumarium, L. Cocklebur. 



August, September. 



tXanthium. spinoaum, L. Spiny Clotbur. 



Abundant in the streets and vacant lots a few years ago, but now becoming for- 

 tunately quite scarce. August. 



Heliopsis laevis, Pers. Ox-eye. False Sunflower 

 August to September. 



tEclipta procumbens, Michx. 



This plant behaves like an introduced weed, tending to invade the streets and 

 gutters. It is rare outside of the city. September. 



tRudbeckialaciniata, L. Cone-flower. 



August, September. 

 Rudbeckia triloba, L. 



Little Falls, rare; the lobed lower leaves generally wanting. July, August. 



Rudbeckia hirta, L. 

 June, July. 



tRudbeckia fulgida, Ait. Brilliant Cone-flower. 



A form was found near the Woodley Park Bridge, with all the rays tubular. It 

 also exhibits the most remarkable variations in the radical leaves. September. 



Helianthus annuus, L. Common Sunflower. 

 Sparingly escaped. August. 



t Helianthus angustifoUus, L. Wild Sunflower. 



Terra Cotta; Reform School. Middle of September. 



Helianthus occidentalis, Riddell. 



Little Falls, on the rocky flats. Early in September. 



t Helianthus giganteus, L. 

 September. 



