512 Our Surroundings 



the largest possible exposure of leaves to the light. Turn the 

 plants several times at intervals of a few days and observe what 

 occurs in each instance. What conclusion do you draw? 



Importance of Seeds to Man. You undoubtedly realize that 

 only through seeds do most plants reproduce themselves. Have 

 you ever considered how important seeds are to man ? The prin- 

 cipal source of the food of the world is from nutrients stored in 

 seeds. Without seeds most of our food plants would vanish and 

 all animal life would be endangered in consequence. The carbo- 

 hydrates, sugar and starch, so necessary to life, made in such a 

 wonderful manner by the green leaves, are stored chiefly in seeds. 

 Likewise the protein food nutrients formed in the plants are stored 

 largely in seeds. Without protein in food, protoplasm, the physical 

 basis of life, cannot be produced. Without carbohydrates, energy 

 in sufficient quantity would not be available. Seeds store and con- 

 serve both these food substances for man. 



SUMMARY 



The most essential part of the seed is the embryo, usually 

 composed of three parts hypocotyl, epicotyl, or plumule, and 

 cotyledon or cotyledons. 



Experiments show that seeds in order to germinate must 

 have food, air, moisture, and a favorable temperature. After 

 germination, the young plants must also have sunlight to insure 

 vigorous growth. 



The importance of seeds to man is apparent when it is borne 

 in mind that the principal source of the food of the world is 

 obtained from nutrients stored in seeds. 



FACT AND THOUGHT QUESTIONS 



1. Describe the structure of the bean seed. 



2. Describe the structure of the corn grain. 



3. Why do many plants fail to grow in winter? 



4. Describe an experiment to show the necessity of oxygen for germina- 

 tion of seeds. 



5. Describe an experiment to show that heat is given off by seeds during 

 germination. 



6. Describe the structure of the embryo in a seed. 



