700 



WEED FLORA OF IOWA 



Fig. 539. Corn Cockle (Agrostemma githago). An immigrant from western 



Asia. 

 (After U. S. Dept. of Agr.) 



(Thlaspi arvense), false flax (Camelina saliva), Berteroa (Berteroa 

 incana and B. mutabilis). These weeds were undoubtedly spread 

 with the cultivation of grain. Many, though by no means all, were 

 brought to Europe with wheat during the early cultivation of grain 

 in Europe. The crusaders undoubtedly were responsible for the 

 spread of these small grain weeds in Europe. Other plants, of 

 which the horseradish is an illustration, were no doubt brought into 

 west Europe as cultivated plants. 



It may not be out of place to give the expression of some of the 

 phytogeographical writers on the subject. 



