444 BOTANY OF CROP PLANTS 



vary somewhat in quality and chemical composition. How- 

 ever, more data are needed to determine the relative feeding 

 value of the different cuttings. 



The alfalfa plant is a heavy feeder. According to Ames 

 and Boltz, a 3-ton yield of alfalfa hay contains 163 pounds of 

 nitrogen, 17 pounds of phosphorus, 99 pounds of potassium, 

 and 90 pounds of calcium. 



Leaves. — The alternately arranged leaves are trifoliate 

 (Fig. 183, E). They are oblong in general outline and sharply 

 toothed along the margin; the tip is terminated by a pro- 

 jecting midrib. The stipules are prominent. 



Inflorescense. — This is a dense raceme springing from the 

 axils of the branches. 



Flowers. — The ordinary color of the flower is purple or 

 violet, but in variegated types, may be blue, green, or yellow. 

 The calyx teeth are longer than the tube of the calyx. The 

 standard is somewhat longer than the wings, which in turn 

 surpass the keel. The staminal tube is held in a state of 

 tension by two opposite lateral projections on the inside of 

 the keel (Fig. 188). 



Pollination (Fig. 188). — Alfalfa possesses a mechanism for 

 the explosive dispersal of its pollen. When the edges of the 

 keel are spread apart, the staminal tube is released, and both 

 the pistil and stamens snap up against the standard. The 

 pollen is scattered in this process. The process is called 

 "tripping." Alfalfa flowers are usually tripped by visiting 

 insects, chiefly bumblebees and leaf-cutting bees {Mega- 

 chile). The weight of an insect may be sufiicient to cause 

 a separation of the keel edges, and consequently "tripping." 

 Usually, however, the separation is brought about by the 

 protrusion of the insect's proboscis between the edges of 

 the keel. It has been observed that alfalfa flowers may be 

 tripped without the visitation of insects. This is termed 



