INTERRELATIONS OF PLANTS AND ANIMALS 35 



substances found in the body wastes from animals are necessary 

 to the life of a green plant. 



Insects and Flowers. — Certain other problems can be worked 

 out in the fall of the year. One of these is the biological interre- 

 lations between insects and flowers. It is easy on a field trip to 

 find insects lighting upon flowers. They evidently have a reason 

 for doing this. To find out why they go there and what they do 

 when there, it will be first necessary 

 for us to study flowers with the idea 

 of finding out what the insects get 

 from them, and what the flowers 

 get from the insects. 



The Use and Structure of a 

 Flower. — It is a matter of common 

 knowledge that flowers form fruits 

 and that fruits contain seeds. They 

 are, then, very important parts of 

 certain plants. Our field trip shows 

 us that flowers are of various shapes, 

 colors, and sizes. It will now be 

 our problem first to learn to know 

 the parts of a flower, and then find 

 out how they are fitted to attract 

 and receive insect visitors. 



The Floral Envelope. — In a 

 flower the expanded portion of the 

 flower stalk, which holds the parts 

 of the flower, is called the receptacle. 

 The green leaflike parts covering the 

 unopened flower are called the sepals. 

 Together they form the calyx. 



The more brightly colored structures 

 are the petals. Together they form 

 the corolla. The corolla is of importance, as we shall see later, 

 in making the flower conspicuous. Frequently the |)etals or 

 corolla have bright marks or dots which lead down to the base of 

 the cup of the flower, where a sweet fluid called nectar is made and 



A section of a flower, cut lengthwise. 

 In the center find the pistil with 

 the ovary containing a number of 

 ovules. Around this organ notice 

 a circle of stalked structured, the 

 stamens; the knobs at tlie end 

 contain pollen. The outer circles 

 of parts arc called the petals and 

 sepals, as we go from the inside 

 outward. 



