Leaf fall of the tuliptree and many others may be delayed when the photoperiod is long. 



profitable production. New and more specifically adapted varieties 

 of soybeans are constantly being selected, so increasing acreages of 

 this very important crop are being grown more economically through- 

 out wider and wider areas. 



Recent experiments to develop sugar-beet seed furnish one of the 

 most striking examples of the possibilities of securing newer and better 

 varieties of a crop that is very sensitive in its responses to photo- 

 period and temperature. Only a few years ago the United States 

 imported from Europe nearly all the sugar-beet seed needed. While 

 developing strains of sugar beets resistant to curly top it became 

 necessary to multiply as rapidly as possible the stocks of seed within 

 the United States. 



Previous experience in the southwestern United States indicated 

 that field plantings made in late summer or early fall would success- 

 fully overwinter and produce seed. This method of production 

 depends in part upon exposure of the plants during winter months to 

 moderately low temperatures. This exposure does not injure the 

 plants, but it preconditions them so that they will develop seed the 

 following summer. Such a procedure eliminates many labor-consum- 

 ing operations characteristic of the European method and results in 

 the efficient production of profitable yields of seed. 



On the basis of the knowledge that the production of sugar-beet 

 seed is favored by long photoperiods, especially at certain tempera- 

 tures or after a rather short exposure to relatively low temperatures, 

 it has been possible to select localities that are much better suited to 



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