Reproduction in Multicellular Plants - 225 



Fig. 12-25. Germinating grains. A, corn grain in early 

 stage of germination. The primary root has penetrated 

 the sheath and is emerging from the grain. B, a later 

 stage in the germination of a corn grain. The primary 

 root has numerous root hairs, and the plump epicotyl 

 has emerged. C, a germinating wheat grain, showing 

 the primary root with hairs, the short blunt epicotyl, 

 and several young side roots. (From Co//ege Botany, 

 by Fuller and Tippo. Holt, Rinehart and Winston, Inc.) 



attracing function of the smaller true petals 

 (for example, in poinsettia and dogwood, Fig. 

 12-27). 



In wind-pollinated flowers (for example, 

 the Cottonwood, Fig. 12-28), petals and sepals 

 are either lacking or inconspicuous, and usu- 

 ally the pistils and stamens occur in separate 

 flowers. Such incomplete flowers are held 

 aloft on the outermost branches of the plant, 

 where there is a maximum exposure to the 

 wind; and usually wind-pollinated flowers ap- 

 pear early in the spring, before the leaves 

 come out to interfere with the transfer of the 

 pollen, which is produced in very large 

 amounts. Most of our common deciduous 

 trees (maples, elms, willows, oaks, etc.) pos- 

 sess wind-pollinated flowers. 



Frequently a multiple cluster of flowers is 

 borne on one stalk (peduncle), which may or 

 may not be branched (Figs. 12-27 and 12-28). 

 Such floral clusters technically are called 

 inflorescences, of which there is a wide va- 

 riety of types. One very common type of 

 inflorescence is possessed by the dandelions, 

 daisies, sunflowers, dahlias, and the other 

 members of a large family, the Compositae. 

 The large "sunflower," for example, is an 

 inflorescence composed of a multitude of very 

 small individual flowers, which are of two 

 sorts (Fig. 12-29). The sterile ray flowers, 

 which lack both pistils and stamens, are ar- 

 ranged radially around the outer margin of 

 the circular head. These ray flowers account 

 for most of the showiness and color of the 

 "sunflower." But the production of seeds is 

 left entirely to the functional disc flowers, 

 which are massed compactly in the central 

 region of the head. 



Variations of Fruit Structure. The enlarged 

 ripened ovule chamber, together with its 

 content of seeds, is a fruit, although in some 

 cases (accessory fruits) other parts originally 

 present in the flower may be incorporated 

 in the fruit. For example, the apple (Fig. 

 12-30) is an accessory fruit of the pome type. 

 In pomes, the receptacle of the flower sur- 

 rounds the ovule chamber and gives rise to 

 the skin and fleshy parts of the pome; and 



