PERTINACITY AND PREDOMINANCE OF WEEDS. 239 



But the test of the theory is, whether weeds and emigrating 

 herbs in general are more self -fertilizing or less subject to 

 cross-fertilization than the majority of related plants, and 

 whether many or any of them are actually self -fertilized 

 through a succession of generations. It seemed to us that, in 

 a limited way, the weeds which Europe has given to North 

 America might answer this question. To keep within bounds 

 and to have a case with all the data unquestionable, we will 

 collate the weeds of European parentage which evince a domi- 

 nating character in the United States east of the Mississippi, 

 referring for the purpose to the " Manual of Botany of the 

 Northern United States " and Chapman's " Flora of the 

 Southern States." The latter, however, adds not a single 

 weed from Europe of any predominance. We include only 

 those which have taken a strong hold and become prominent 

 either by their general diffusion over the area or by taking 

 marked possession of certain districts. For examples of the 

 latter take Echium vulgare in Virginia, Ranunculus bulbosus 

 and Leontodon autumnale in eastern New England, and Ge- 

 nista tinctoria, which covers certain tracts in the eastern part 

 of Massachusetts, although nearly unknown elsewhere. We 

 must include several species which as weeds came from Eu- 

 rope, although they are probably, some of them undoubtedly, 

 indigenous to some part of the United States* 



The following are the herbaceous plants naturalized from 

 Europe and of an aggressive character in the Atlantic United 

 States. Herbs of recent introduction, and those of however 

 ancient naturalization which have not either spread widely or 

 increased greatly over a considerable district, are omitted. 



The eighteen species in italic type, nearly half of them 

 Grasses, are probably indigenous to some portions of North 

 America. In some cases the introduced and the indigenous 

 plants have come into contact. 



Ranunculus bulbosus. Raphanus Raphanis- Silene inflata. 



Ranunculus acris. trum. Lychnis Githago. 



Nasturtium officinale. Capsella Bursa-pastoris. Stellaria media. 



Sisymbium officinale. Reseda Luteola. Portulaca oleracea. 



Brassica Sinipistrum. Saponaria officinalis. Malva rotundifolia. 



