FORAGE PLANTS OF .THE FAMILY LEGUMINOS^E 



189 



untripped 



tripped 



The staminal tube of ten, diadelphous stamens is held in a state of tension 

 by two opposite lateral projections arising from the inside of the keel. 

 This mechanism brings about the explosive discharge of the pollen, when 

 the staminal tube is released, and the pistil and stamen snap up against 

 the standard and this process is 

 known as "tripping." Bumble- 

 bees and leaf-cutting bees are 

 usually the "trippers" of alfalfa 

 flowers (Fig. 78). Insect visita- 

 tion induces cross pollination, 

 but automatic release of the 

 floral parts by the action of 

 humidity and temperatures re- 

 sults in self pollination. An 

 abundance of insect life usually 

 increases the output of seeds. 

 Other conditions of climate and 

 cultivation also influence seed 

 production. The alfalfa fruit is 

 a spirally coiled pod with two or 

 three coats. Each pod contains 

 from one to eight kidney-shaped 

 seeds about ^ inch long, which, 

 retain their vitality for many , 

 years (Fig. 77). 



Varieties. There are a con- 

 siderable number of varieties of 

 alfalfa in cultivation. There is 

 a hardy variety suitable for 



FIG. 78. Pollination of alfalfa. A, flower 



unfnpped 



tripped 



,,. untripped with calyx and standard removed; 

 ims B, same tripped; C, position of staminal tube 



growth in the cold northwest 

 known as Grimm alfalfa. 



hardiness may be due to a Strain untripped and tripped. (Robbins after U. S. 



of the yellow-flowered alfalfa Dept ' AgrL) 



(Medicago falcata). There is the sand lucern and variegated alfalfa and 

 varieties designated by the names of the countries of their derivation, as 

 the American, Arabian, German, Peruvian and Turkestan varieties. 

 The Turkestan variety is well-adapted to drought resistance. Arabian 

 alfalfa is suited to warm conditions, as in Arizona and Texas, while 

 Peruvian alfalfa is adapted to countries where irrigation is practiced. 



