88 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



may be attached to it. The chief use of the fruit is to hold and to 

 protect the seeds ; it may ultimately distribute them where they 

 can reproduce young plants. 



Each seed has been formed as a direct result of the fertilization 

 of the egg cell (contained in the embryo sac of the ovule) by a 

 sperm nucleus of the pollen tube. 



Practical Exercise 10. Describe with the aid of diagrams the growth into 

 a fruit of some flower, not given in the text. 



Self-Testing Exercise 



In a pod, the seed is fastened to the ovary wall by the (1). 



The (2) is the part of the wall of pod that bears the 



(3). The pod is a (4) (5) and is called a 



(6). The chief use of the (7) is to protect the 



(8) . Seeds are formed as a direct result of the (9) 



of the (10) cell in the embryo sac by the (11) nu- 

 cleus in the (12) tube. 



PROBLEM IX. WHAT ARE SOME ADAPTATIONS IN INSECTS 

 FOR CARRYING POLLEN? 



Insects as pollinating agents. Insects often visit flowers to 

 obtain pollen as well as nectar. In so doing they may transfer 

 some of the pollen from one flower to another of the same kind. 

 This transfer of pollen, called cross-pollination, is of the greatest 

 use to the plant, as we shall see later. Sir John Lubbock observed 

 bees and wasps to learn how many trips they made daily from their 

 homes to the flowers, and found that a wasp went out on 116 visits 

 during a working day of 16 hours, while a bee made ^almost as 

 many visits and worked almost as long as the wasp. It is evident 

 that in the course of so many trips to the fields a bee must light 

 on hundreds of flowers. 



Nectar and nectar glands. The bee is attracted to a flower for 

 food. This food may consist of pollen or nectar. Nectar is a 

 sugary solution that is formed in the flower by little collections 

 of cells called the nectar glands. The nectar glands are usually 

 so placed that to reach them the insect must first brush the stamens 

 and pistil of the flower. Frequently the location of the nectaries 

 (nectar glands) is made conspicuous by brightly colored markings 



