2Il] FLORA OF COLUMBIA AND VICINITY 69 



men to all ruderal associations. In the treatment that follows 

 certain natural assemblages of weeds are described as associa- 

 tions, though these can have little permanence as such, since a 

 plowing under, or a rotation of crops, may bring about a quite 

 different assemblage of weeds on the same ground the following 

 season. 



a. Ruderales cirsioides. The thistle association of 

 pastures and old fields consists of tall herbs with foliage dis- 

 tasteful to cattle, whether through spiny foliage as in the thistle 

 (Cirsiuni spp.), the woolly covering of the leaves as in the mul- 

 lein (Verbascum Thapsus), and the cudweeds (Gnaphalium 

 spp.), the vile smell as in the hound's-tongue (Cyttoglossum of- 

 ficinale), or some poisonous or bitter principle as in the scoke 

 (Phytolacca decandra) and the Jimson weeds {Datura spp.). 

 Plants of acrid milk}' juice are common, such as species of As- 

 clepias, Apocyniim, Euphorbia, and Lactuca. Ruderal grasses 

 are frequent also, and these, too, are kinds that cattle avoid, 

 while better herbage is obtainable. 



b. Ruderales erigerontoides. The fleabane associa- 

 tion of meadows consists largely of Erigeron anniius, E. ramo- 

 sus, Rudbeckia hirta, Otmgra biennis, Achillaea Millefolium, 

 certain chesses (Bromus spp.), and docks and sorrel (Rumex 

 spp.). The pasture weeds are frequent also, as are species of 

 Vernonia, Verbena, and Teucrium. 



c. Ruderales bromoides. The chess association of 

 grainfields occurs also along roadsides, where it reaches its best 

 development in the region. Little wheat is grown, but where 

 such fields are found, Bromus secalinus and Agrostemma Gi- 

 thago are the characteristic weeds. With them occur certain 

 speedwells (Veronica spp.), the shepherd's-purse (CapseUa 

 Bursa-pastoris), the red-root or gromwcU (Lithospermum ar- 



