Xll TABLE OF CONTENTS 



UNIT XVI. HOW DOES MAN CONTROL HIS EN- 

 VIRONMENT FOR WEALTH? 



I. How Are Plants Used as Food? 520 



II. What Are Other Economic Values of Plants? . . . 528 



III. What Is the Value of Animals as Food for Man? . . 530 



IV. What Are Other Economic Values of Animals? . . 537 

 V. What Harm Is Done by Animals? 544 



VI. What Is the Economic Importance of Birds? . . . 547 



VII. How Can We Recognize Some Common Birds? . . . 551 



VIII. What Is the Economic Importance of Insects? . . 560 



UNIT XVII. HOW DOES MAN CONSERVE HIS 

 NATURAL RESOURCES? 



I. What Are the Values of Trees? . . . . 574 



II. Why Is the Conservation of Forests Necessary? . . 579 



III. What Is Being Done for the Conservation of Fish and 



Other Aquatic Animals? . . . . . . . 587 



IV. What Is Being Done for the Conservation of Birds? . 594 

 V. What Is Being Done for the Conservation of Mammals? 598 



VI. How Is Conservation Applied to Man? .... 599 



UNIT XVIII. HOW DOES MAN CONTROL THE IM- 

 PROVEMENT OF LIVING THINGS? 



I. How May Environment Affect Plants and Animals? . 608 

 II. How Do Living Things Reproduce and Develop? . .611 



III. What Are the Laws of Heredity? ..... 620 



IV. What Determines Heredity? 626 



V. How Are New Varieties of Plants and Animals Pro- 

 duced? 631 



VI. How Do the Laws of Heredity Apply to Man? . . 636 



UNIT XIX. HOW MAY BIOLOGY AID IN MY OWN 

 IMPROVEMENT? 



I. How Can I Choose a Vocation? 646 



II. For What Vocations May Biology Help Prepare Me? 649 



UNIT XX. WHO ARE SOME OF THE MAKERS OF BIOLOGY? 



I. Who Were Some Early Workers in Biology? . . . 657 



II. Who Were Some of the Conquerors of Disease? . . 659 



III. What Are Some Great Names in the Study of Progres- 



sive Development? ........ 665 



IV. What Are Some Great Names in Natural History? . 668 

 V. What Are Some Great Names Connected with Plant and 



Animal Breeding? 670 



