WEED MIGRATION 



695 



heliotrope (Phacelia sericea), stone crop (Sedum stenopetalum) , 

 arnica (Arnica cordifolia) . During the first year the vegetation is 

 frequently widely scattered, much depending on the source of the 

 seed. The lodge pole pine may not reappear on the burnt area 

 for a long time. Here again much depends on the distance from 

 which the seed has to come. 



An Iowa forest, burned over, is covered by bull thistle (Cirsium 

 lanceolatum) , fireweed (Erechtites hieracifolia) , horseweed (Erige- 

 ron canadensis) , whiteweed (Erigcron anmius), followed later by 

 small perennials, as blue grass, goldenrods. asters and sunflowers ; 

 then hazel, coral berry, hawthorns, elms, poplars, maples and oaks. 



J. Burtt Davy* in an interesting account of alien plants spon- 

 taneous in the Transvaal enumerates 141 species alien to that part 

 of Africa ; of these 15 are now so cosmopolitan that their original 

 home is not known. Two were unidentified. The origin of these 



Fig. 536. Lamb's Quarters (Chenopodium album). A common foreign weed. 



Native to Europe. 



♦Rep. S. Afr. Ass. Adv. Sei. 1901 : 252-299. 



