352 FORAGE PLANTS AND THEIR CULTURE 



greater hardiness and rootstock-producing tendency of 

 the former, combined with the better seed-production and 

 superior habit of the latter, are characters highly desirable 

 to combine. 



While breeders have already developed various promis- 

 ing improved alfalfas, none of these has yet become estab- 

 lished commercially. 



417. Breeding methods. In connection with the 

 improvement of alfalfa by breeding, certain special 

 methods will be found useful. Due to the readiness with 

 which natural crossing takes place, a large proportion of 

 alfalfa plants are heterozygote ; that is, do not breed 

 true even when the seed is produced by bagged or caged 

 flowers. On this account a progeny row of each selected 

 plant should be grown from seed produced under bag to 

 determine whether it will breed true to type. 



For the rapid multiplication of a selected plant, two 

 methods may be used : First, new plants can readily be 

 produced either from cuttings, or, where rootstocks are 

 present, by division; second, pure seed can be secured 

 by growing the plants in cages to exclude insects, and 

 tripping the flowers by pressure of the hand. 



Increase plots of a selected strain must be grown at a 

 considerable distance from any other alfalfa, otherwise 

 crossing will be effected by bees. 



418. Weeds. In many places weeds constitute a 

 serious drawback to alfalfa culture. 



Kentucky blue-grass is probably most troublesome to 

 established fields in Ontario and the Eastern States. Heavy 

 liming so necessary for alfalfa also favors blue-grass, which 

 usually appears by the second year, and unless restrained 

 will kill out half of the alfalfa by the third or fourth year. 

 In the northern part of the irrigated regions, blue-grass 



