UNIVERSITY 

 PRAIRIE FLOWERS IN 



the pollen out before itself. Thus the yellow hats are 

 formed. 



But the style is not yet split, and is not ready to be 

 fertilized. Only after most of the pollen has been brushed 

 away by insects does it split, and the upper sides of the 

 little horns, which are yellow or dark purple, are now ready 

 to be fertilized by pollen from the florets. 



Students of botany have found that it is an advantage 

 to most plants if their flowers do not fertilize themselves, 

 but are cross-fertilized by insects, or some other agency. 

 In cross-fertilization the pollen of one flower is carried to the 

 pistil of another. Many flowers have exceedingly flne and 

 interesting devices for preventing self-fertilization and for 

 securing cross-fertilization by insects. In some plants, as, for 

 instance, in our well-known milkweeds, self-fertilization is 

 absolutely impossible. Some flowers are self-fertilized only 

 when insects are scarce ; others are wind-fertilized ; and 

 some are always self-fertilized. Can you tell now by what 

 means the sunflower secures insect-fertilization and pre- 

 vents self-fertilization? Do the pistil and the anthers in 

 one floret mature at the same time ? 



On top of the immature seeds you discover two small 

 scales ; these really are the calyx for one floret. In many 

 composites this calyx is changed to hairs, or feathers, or 

 awns ; it is called pappus. 



The common floor on which the florets are set is called 

 the receptacle. It is often covered with chaff-like scales, 

 which probably protect the seeds and help to hold them in 

 place. We have already learned that all the florets are 

 surrounded by a common calyx, which consists of rather 

 large leafy scales, often arranged like shingles on a roof. 

 This common calyx is called the involucre. 



Have a druggist weigh for you one sunflower seed. You 

 will find that it weighs about a grain. Then weigh on a 



