VI PREFACE 



be used to organize the work of superior students who have a basic 

 knowledge of the material of the unit and who may therefore be 

 allowed to organize some project as their share of the class work. 

 The preview follows, giving a brief introduction to the problems of 

 the unit, and is both an organizing and a motivating device. Next 

 come the problems, many of which are introduced by laboratory 

 exercises or demonstrations, with opportunity for individual work 

 where it is practical. Numerous exercises and problem questions 

 give opportunity for individual pupil assignments and reports. 

 The organization of the unit by the pupil is provided for in the 

 outline summaries, in the attainment tests, in individual check-up 

 on the answers to the survey questions, and in the self-testing 

 exercises. In these ways the teacher has an opportunity for 

 individual work with students. The recitation period may consist 

 of individual reports on rather large blocks of the unit, interspersed 

 with rapid-fire questions where it is obvious that the student 

 organization of the topic has left unexplained some vital point. 

 The author wishes to thank the following for their critical 

 reading of the manuscript in its entirety or in part or who have 

 made valuable suggestions: Charles W. Finley, State Teachers 

 College, Upper Montclair, New Jersey; Frank M. Wheat, Head 

 of Department of Biology, George Washington High School, New 

 York; Paul B. Mann, Evander Childs High School, New York; 

 Ada L. Weckel, Head of Department of Science, High School, 

 Oak Park, Illinois; Annah P. Hazen, Head of Department of 

 Biology, Eastern District High School, Brooklyn, New York; 

 and George W. Hunter III. Thanks are also due Loran W. Kitch, 

 Herbert Hoover High School, Glendale, California ; Roy Knapp, 

 Burbank Junior High School, Miss Beatrice Cayo, Elsinore High 

 School, Elsinore, California; Mrs. Karyn B. Sanders, Downey 

 Union High School, Downey, California; and Wright Pierce, 

 Claremont, California, who have read the proof and given sugges- 

 tions on teaching devices. 



