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.) 
Fic. 24.—.41, flower from 
the head of Dandelion. a, 
strap-shaped corolla; b, calyx 
a made up of many slender hairs 
B C known as pappus; p, base of 
pistil; s, stamens forming a 
Fic. 23. — Flowers of the Yarrow (Achillea tube around the upper part of 
millefolium), a Composite. A, a head of the pistil. 3B, tubular flower 
flowers sectioned, showing the strap-shaped and fruit of Beggar’s Tick 
flowers around the margin and the tubular showing tubular corolla (a) and 
flowers occupying the central region of the the calyx (b) consisting of two 
head. B and C are tubular and strap- spiny tceth which persist and 
shaped flowers more enlarged aid in scattering the fruit. 
This process of releasing the stamens and pistil, known as 
“ 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, 
