38 BULLETIN 428, U. S. DEPARTMENT OF AGEICULTTJRE. 



PERIODS OF GROWTH. 



Observations made at Brookings in 1912, 1913, and 1914 indicate 

 that Medicago falcata has a tendency to commence growth earlier in 

 the spring than Medicago sativa or Medicago sativa X falcata 

 hybrids. This characteristic is apparently influenced by climatic and 

 soil conditions. If, as frequently happens in early spring, a short 

 period favorable for growth is followed by continued cool or cold 

 weather, the difference between the quantity of growth of Medicago 

 falcata and Medicago sativa when the growing season really begins is 

 very noticeable. This probably is due to the fact that while both may 



Fig. 17. 



-Loose bunches of stems of various forms of Medicago falcata, showing general 

 types of growth. 



start during the favorable period, the former is able to outgrow the 

 latter during the unfavorable period following. 



At Highmore, S. Dak., in the spring of 1912, Medicago falcata con- 

 tinued growth throughout an extended period of very cold weather, 

 while Medicago sativa made very little growth. The same phenome- 

 non was observed at Brookings, but the difference between the two 

 was not so pronounced. In the spring of 1914 the difference in the 

 earliness of growth was less noticeable than in the other seasons men- 

 tioned. The soil was extremely dry until well into April that year, 

 after which the conditions of warmth and moisture were unusually 

 favorable, resulting in good growth of all varieties. It seems reason- 

 able that the lack of difference between the spring growth of Medi- 



