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 {Erigeron annuus), 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. 5'36. 



Lamb's Quarters (Chenopodium albuw,). 

 Native to Europe. 



A common foreign weed. 



•Rep. S. Afr. Ass. Adv. Sci. 1901 ; 252-299. 



