118 PLANT GROWTH 



Composite flowers, known as the sunflower type, such as 

 the sunflower, zinnia (Fig. 20, A), and dandelion, grow in 

 heads. Each part is a true flower with a smaU inconspicuous 

 calyx of hairs, bristles, or bracts, called pappus. In the 

 dandelion it becomes the group of hairs attached to the ripe 

 seed. The corolla is of two kinds; as illustrated in the zinnia, 

 each broad petal-like structure is a group of five united 

 petals, called a ray flower (Fig. 20, B and C). The center 

 has numerous flowers with the petals united to form small 

 tubular disc flowers (Figs. 20, B, D, and E). D shows the 

 bract common on many composite flowers. Dandelions have 

 only ligulate flowers. The five stamens have their anthers 

 united to form a tube around the style (Fig. 20, E, shows the 

 flower opened to display the stamens and pistil) . The pistil 

 has a two-parted stigma and an ovary which bears a single 

 seed. The seed remains in the ovary which is planted as a 

 seed. 



The grass flowers grow in groups called spikelets. They 

 are so small that they are not recognized as being common 

 to all our grasses including corn and other cereals. Each 

 spikelet has a pair of scale-like parts called glumes, between 

 which the one or more flowers are located. Each flower has 

 a pair of scales which enclose the three stamens and the pistil. 

 The pistil has a two-parted plumose stigma and an ovary 

 with a single seed. A single corn kernel with its silk ending 

 in the divided stigma is the pistil. At the base of the flower 

 are two small bodies called lodicules which swell and push 

 the pair of scales apart at the time of pollination. The flower 

 structure is easily visible and delicately attractive when 

 shedding pollen. 



The pollen is borne in great abundance in the stamens, 

 several millions of the cells or pollen grains being produced 

 by a single plant. In a few plants, such as the orchids, it 

 sticks in masses, but in most plants the individual grains 

 form a powder or dust. Each pollen grain is a single cell with 



