24 



FLOWERS 



banner; the two side pieces, known as wings; and the single 

 boat-shaped portion beneath the wings, known as the keel. In 

 the Red Clover flower shown in Figure 21 , these parts are pointed 

 out. The stamens and pistil are entirely enclosed by the keel, 

 and when pressure is exerted on the keel, the stamens and pistil 

 spring out of their enclosure with considerable force. (Fig. 22.) 



B <- 



FIG. 23. Flowers of the Yarrow (Achillea 

 millefolium), a Composite. A, a head of 

 flowers sectioned, showing the strap-shaped 

 flowers around the margin and the tubular 

 flowers occupying the central region of the 

 head. B and C are tubular' and strap- 

 shaped flowers more enlarged 



FIG. 24. A, flower from 

 the head of Dandelion, a, 

 strap-shaped corolla; 6, calyx 

 made up of many slender hairs 

 known as pappus; p, base of 

 pistil; s, stamens forming a 

 tube around the upper part of 

 the pistil. B, tubular flower 

 and fruit of Beggar's Tick 

 showing tubular corolla (a) and 

 the calyx (6) consisting of two 

 spiny teeth which persist and 

 aid in scattering the fruit. 



This process of releasing the stamens and pistil, known as 

 11 tripping the flower," is mainly the work of insects and is im- 

 portant, because in some of the Legumes the flowers will produce 

 no seed unless tripped. 



Composite Flowers. There is a large group of plants to 

 which Lettuce, Dandelions, Sunflowers, Beggar's Tick, Thistles, 



