578 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



ences in time of maturity when carried into temperate regions 

 where decided seasonal change in length of day occurs. This, in 

 fact, has proved to be the case in a number of instances where seed 

 of tropical plants have been brought into this country. Thus it 

 may happen that a culture which seems to consist of a pure variety 

 as grown in the Tropics, can be readily separated into two or more 



/& 32 "Off &? &o 



£>/<?s(S /Vr&~? *&?/£ ofc? 72? G£y?/*7/A<>4r/C>A/ 



se 



/£? 



Fig. 2. — Graph showing the shortening of the vegetative period preceding flowering in soy 

 bean which results from progressively later planting during the growing season. 



distinct strains or varieties when grown in higher latitudes, these 

 new forms showing marked differences in time of maturity. In high 

 latitudes an early-maturing variety of soy bean is one which flowers 

 a#j}} Afrits under the influence of long days, while a late variety 

 fl<^rs$nd fruits in response to short-day influences. That these 

 relationships have an important bearing on problems in plant 

 breeding is evident. 



