278 



BOTANY. 



three forms of petals in each flower, viz., one large 

 broad one, the "banner," two lateral ones, the "wings," 

 and two anterior ones which together form the "keel." 

 These all together form a structurs enclosing the stamens 

 and pistil in such a way that an insect cannot get any of 

 the nectar at the base of the corolla without setting free 

 some of the pollen, which adheres to the hairs of its body 

 and is thus carried to the stigma of some other flower. 



527. In the Gamopetalse the union of petals into a tube 

 serves to compel insects to visit the flower in one way 

 only. In the Mints (Fig. 166) the flower is two-lipped. 



■i^V' 



Fio. 166.— Flower of Dead-nettle, (Lamium) aide view and vertical sec- 

 tion. Magnified. 



the broader lip usually serving as a resting-pkce for the 

 insect while it thrusts its head or tongue into the corolla. 

 The upper lip is frequently arched so as to contain the 

 stamens and style. In the Dead-nettle the stigma projects 

 beyond the stamens (Fig. 166), so that upon visiting suc- 

 cessive flowers the insect always first pollinates the stigma 

 with pollen from preceding flowers, and then, coming in 

 contact with the stamens, secures more pollen. In many 

 plants with a similar structure the stamens mature before 



