192 THE PLANT LIFE OF MARYLAND 



yards, while Datura taiula and Xanthium canadense are apt to pre- 

 fer rubbish piles. 



Weeds. — The majority of the noxious weeds found in fields while 

 under cultivation are of foreign origin. The Bermuda grass, *Cap- 

 riola dactylon, is especially common in the drier parts of Southern 

 Marvland. On the truck farms of Anne Arundel County *Echium 

 vulgare, *Amaranthus retroflexus, *Chenopodium album, "Portu- 

 laca oleracea, with the grasses * Syntherisma sanguinalis, *Ixophorus 

 glaucus, *Panicum crus-galli, Oenchrus tribuloides are more or less 

 plentiful. Near Baltimore a field badly infested by *Brassica 

 arvensis was seen. *Plantago lanceolata. Solatium carolinense, 

 *Daucus carota, Ambrosia artemisiaefolia are only trio common 

 throughout the region. If a field is allowed to rest from cultivation 

 for a year, native species begin to gain the ascendency. In the 

 earlier part of the season a society is apt to appear in which no 

 one species prevails; it may include '"'Allium vineale, ''Uamex ace- 

 tosella, *Trifolium arvense, Diodia teres, *Plantago lanceolata, 

 Cassia chamaechrista, and many others. A little later *Daucus carota 

 may become dominant, and still later a field may be practically cov- 

 ered by Ambrosia artemisiaefolia. The history of such a field in 

 succeeding years may show great variation. Even in a pasture as 

 is pointed out by DeVries* the same grasses do not grow year after 

 year, but the sorts which are dominant depend on climatic features 

 such as rainfall and temperature at the time of year which may lie 

 critical for any particular species. In the southern part of our 

 district, fields which had lain idle for one or more years were found 

 to be occupied by Leptilon canadense, others with Monarda punctata, 

 while still others were largely covered by Onagra biennis or by 

 Eufhamia graminifolia. Other plants common in such areas are 

 ^Allium vineale, *Trifolium arvense, Strophostyles umbellata, 

 Strophostyles helvola, *Daucus carota, Lepidium virginicum, Oxalis 

 slrirla,*Plantago lanceolata, *~Verbascum thapsus, *Echium vulgare, 

 Erigeron ramosus, Ambrosia artemisiaefolia, Achillea millefolium. 

 In case a neglected field is very sandy, the dominant plants are apt 

 to be "Chondrilla juncea, Euphorbia corollata, Diodia teres, Cen- 



*DeVries, H. Species and Varieties, their origin by Mutation, p. 103. 



