46 



BULLETIlSr 428, U. S. DEPARTMENT OF AGRICULTURE. 



neath the surface of the soil and in certain cases to produce true pro- 

 liferating lateral roots, and its ability to suspend activity and to 

 lessen transpiration by reducing its leaf surface. During periods of 

 severe drought it makes very little growth above ground, but appar- 

 ently devotes some energy to the production of rhizomes, from which 

 new growth develops either with the resumption of favorable condi- 

 tions the same season or in the following spring. This adaptation is 

 of considerable benefit in carrying plants through the critical periods 

 of summer. 



The following heretofore unpublished data on the water require- 

 ment of Medicago falcata^ b}^ which is meant the quantity of water 

 required by the species to produce a given amount of dry matter, as 

 determined by the method of Briggs and Shantz, have been fur- 

 nished by Mr. A. C. Dillman, of the Office of Alkali and Drought 

 Resistant Plant Investigations. 



A summary of the water requirement of Medicago falcata as compared with 



that of Medicago sativa (the Grimm variety), as determined at Newell, S. 

 Dak., for four seasons, 1912 to 1915, inclusive, and at Akron, Colo., in 1914, is 

 given in the following table : 



Table VI. — Comparative water requirement of Medicago falcata and Medicago 

 sativa at Neioell, S. Dale, in 1912 to 1915, inclusive, and at Akron, Colo., in 

 1914. 





Water requirement based on dry matter. 



Place, year, and species. 



Actual. 



Relative. 





First 

 crop. 



Second 

 crop. 



Third 

 crop. 



Combined 

 crops. 



First 

 crop. 



Second 

 crop. 



Third 

 crop. 



Com- 

 bined 

 crops. 



At Newell, S. Dak. 

 Season of 1912: i 



622 ±15 

 699±15 



340± 7 

 469± 6 



603±38 

 539 



399± 8 

 424 ± 9 



735 ±18 

 772±18 



713±11 

 817 ±13 



930±26 

 800 



424 ± 4 

 413 ± 7 





663±12 

 735 ±15 



579±12 

 735 ± 8 



687 ±20 

 669 



541 ± 9 

 499 ± 7 



89 

 100 



73 

 100 



93 

 100 



94 

 100 



87 

 100 



107 

 100 



91 

 100 



95 

 100 



87 

 100 



116 

 100 



103 

 100 



100 

 100 



84 

 100 



97 

 100 



109 

 100 



176 

 100 



142 

 100 



114 

 100 



133 

 100 



90 







100 



Season of 1913: 



1,220±52 

 1,115±16 



79 





100 



Season of 1914: 2 



103 







100 



Season of 1915: 



1,108±20 

 630±18 



108 





100 



Mean at Newell: 



95 













100 



At Akron, Colo. 

 Season of 1914: 1 



652±16 

 610± 3 



757 ±13 

 907 ±14 



1,201 ±75 

 1,055±12 



848 ±27 

 890 ± 6 



95 





100 



Mean at both Newell and 

 Akron: 



95 













100 















1 The data at Newell, S. Dak._, in 1912, and at Akron, Colo. , in 1914, were procured from seedling plants, 

 while those obtained at Newell m 1913 to 1915, inclusive, were from plants a year or more old. 



2 At Newell, S. Dak. , in 1914 there were five pots of Medicago falcata, but only one pot of Medicago sativa. 



