568 



Journal of Agricultural Research voi. xviii, no. h 



developing new axillary branches. The new growth finally developed 

 flower heads; and thus the plants blossomed for the second time during 

 the first half of September, which is the time of blossoming of the original 



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Fig. I.— Graph showing the shortening of the vegetative period preceding flowering in soybeans which 

 results from progressively later planting during the growing season. 



controls exposed to the normal daylight period throughout their develop- 

 ment. 



The ragweed, likewise, resumed vegetative development after a time, 

 and, in fact, under the influence of the full length of the daylight period 

 the new growth exceeded in size that of the original plants. The plants 

 blossomed the second time during the last week in August, which is also 

 the time of blossoming of the original controls and of ragweed growing 

 in the field. It may be noted, however, that while the original growth 

 produced staminate spikes as well as pistillate flowers in the usual man- 



