Acknowledgment is also made to the following for various cuts: Henry J. Green, Brooklyn, New York; Julien P. Friez, Baltimore, Maryland; C. H. Stoelting Co., Chicago, Illinois; Draper Manufacturing Co., New York city; Gundlach-Manhattan Optical Co., Rochester, New York; Rochester Optical Co., Rochester, New York; Bausch and Lomb Optical Co., Rochester, New York. FREDERIC EDWARD CLEMENTS. The University of Nebraska, May, 1905. CONTENTS CHAPTER I. THE FOUNDATION OF ECOLOGY THE NEED OF A SYSTEM PAGE 1. The scope of ecology 1 2. Ecology and physiology 1 Historical Development 3. Geographical distribution 2 4. The plant formation 2 5. Plant succession 3 6. Ecological phytogeography 4 7. Experimental ecology 4 8. Ecology of the habitat 5 9. The evidence from historical development 6 Present Status of Ecology 10. The lack of special training 6 11. Descriptive ecology 7 12. The value of floristic 8 13. Reconnaissance and investigation 8 14. Resident investigation 9 15. The dangers of a restricted field 9 Applications of Ecology 16. The subjects touched by ecology 10 17. Physiology and pathology 11 18. Experimental evolution 11 19. Taxonomy 12 20. Forestry 14 21. Physiography 15 22. Soil physics 15 23. Zoogeography 15 24. Sociology 16 THE ESSENTIALS OF A SYSTEM 25. Cause and effect: habitat and plant 16 26. The place of function 17 CHAPTER II. THE HABITAT CONCEPT AND ANALYSIS