442 BOTANY OF CROP PLANTS 



ovary is sessile or short-stipitate, and several- or rarely one- 

 ovuled; it has a subulate (awl-shaped), and smooth style. 

 The pods (Fig. 187) are curved or spirally twisted, veiny or 

 spiny, and indehiscent. 



Geographical. — There are a number of species of Medi- 

 cago, all of which are native to the eastern hemisphere. They 

 naturally range from Eastern Asia to Southern Africa. 

 There are seven perennial species of Medicago, and about 37 

 annual species, one of which, yellow trefoil {Medicago lupu- 

 lina), has a biennial or possibly perennial form. The non- 

 perennial species are commonly known as "bur clovers." 

 They will grow naturally as winter annuals. 



Key to Principal Species of Medicago 



Perennial, erect-growing plants; flowers violet, Medicago saliva (alfalfa). 

 Annual, low-growing plants; flowers yellow. 

 Pods kidney-shaped, without spines, Medicago lupulina (hop clover). 

 Pods cylindrical, with spines. 



Stems pubescent; pods i\i to s millimeters diameter; purple spot in 

 center of each leaflet; two to eight seeds in each pod, Medicago arabica 

 (spotted bur clover). 

 Stems glabrous, pods 7 to 10 millimeters diameter; no purple spot in 

 center of each leaflet; three to five seeds in each pod, Medicago 

 hispida (toothed bur clover). 



MEDICAGO SATIVA (Alfalfa, Lucerne) 



Roots. — Alfalfa is a deep feeder. The young plant usually 

 sends down a single tap root. As a rule, this takes a straight 

 downward course. Comparatively few side roots are given 

 off. Usually, these are below the depth of 4 feet. Headden 

 found in a plant only nine months old, that the young roots 

 had extended to a depth of over 9 feet. Ordinarily the weight 

 of roots exceeds weight of top. 



Stems. — ^Alfalfa is an ascending or erect perennial. Its 

 life period is dependent upon environmental conditions and 



