312 CHAPTERS ON EVOLUTION. 



find that a corolla is wanting, although a calyx (Fig. 209, c) is present. 

 Again, in the willow, which, like the greater nettle, has its stamens 

 and pistils (Figs. 210 and 211) on different plants, there appears to 

 be no " flower" in the ordinary sense of the term ; and the calyx as " 

 well as the corolla is found to be wanting in these trees. 



The stamens, just mentioned, form the third set of organs proper 

 to the perfect flower. Looking at buttercup, wall-flower ( Fig. 205, st\ 

 saxifrage (Fig. 215) or campanula (Fig. 214), we readily see the 

 stamens. They exist as stalked organs (Fig. 214, ss), each con- 



FIG. 212. MALE OR STAMINATE FLOWERS OF OAK. 



sisting of a stalk or filament (Figs. 216, 217, ,$/), and a head called 

 the anther (a). The head is hollow and contains the fine yellow 

 dust termed pollen, which, at the time of ripening, is usually found 

 scattered conspicuously about the interior of most flowers. The 

 fourth and central set of organs found in the flower constitute the 

 pistil (Figs. 214, 215, and 218) or seed-producing structure. This 

 organ is composed of one or more parts called carpels. Each 

 carpel consists in turn of a lower distended part called the ovary 

 (Fig. 218, cv\ within which the ovules are produced; of a neck 

 or filament, the style (sf) ; and of a head borne on the style (sg), 

 and named the stigma. The style or stigma may be absent ; but in 

 the great majority of flowers both parts are present, the ovary being 



