Mar I, 1920 



Effect of Length of Day on Plant Growth 



569 



ner, the second growth produced pistillate flowers almost exclusively and 

 the leaves were mostly atypical. 



RELATION OF DATE OF PLANTING TO DATE OF BLOSSOMING IN 



SOYBEANS 



Through the spring and summer of 19 19 a series of plantings of soy- 

 beans which included the four varieties used in the tests described above 

 were made in the field at regular intervals of three days as nearly as 

 conditions would permit. All plantings of each variety consisted of 

 rows 10 feet in length. The date recorded as that when first blossoms 

 appeared is in each case that when the majority of the individuals in the 

 planting first showed one or two open blossoms. In most instances the 



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Fig. 2.— Graph showing changes in length of day during the growing season in the latitude of Wash- 

 ington, D. C. Ordinates indicate 2-hour intervals of the day and abscissae indicate i6-day periods 

 of the growing season. 



greater number of the individuals in a planting showed their first open 

 blossoms on practically the same date. The dates of planting, germina- 

 tion, and appearance of first blossoms, together with the number of days 

 from germination till blossoming are shown in Table I. 



The effect of the date of planting on the length of the period from 

 germination to the blossoming stage for each variety is more easily seen 

 in the curves of figure i , in the construction of which the number of days 

 from April 30 to dates of germination are used as ordinates and the num- 

 ber of days included in the periods of growth prior to blossoming are used 

 as abscissae. The relative length of the day — that is, the time between 

 sunrise and sunset, expressed in 2-hour periods — also is shown for the 

 same period in figure 2. The relative heights of the plants in the con- 

 secutive plantings of the Biloxi variety are shown graphically in figure 3. 



1601 1 5 * — 20 a 



