PREFACE 



The modern textbook in elementary science must do several 

 things. First of all, it must contain enough subject matter to 

 permit a rather wide choice of material ; this because of differences 

 in the environment in which the book is used. Obviously every 

 teacher of biology would like a text that interprets the particular 

 environment in which the teaching is done, but since this is an 

 impossibility the solution of the problem is a wide choice of topics. 

 This text gives a large selection of informational material. 



Second, the modern text must give to the teacher a variety of 

 problems, demonstrations, projects, and exercises for the workbook 

 in order that the need of the individual student may be adequately 

 met. Nothing is more difficult for the overloaded teacher than to 

 attempt to adjust the work to the individual needs of a large num- 

 ber of pupils. This book, with its many exercises and questions, 

 graded to the needs of a heterogeneous group, squarely meets the 

 problem of individual variation. Projects, demonstrations, and 

 reports are suggested also in sufficient numbers to fill the time of a 

 widely diverging group. 



Another thing the modern text should do is to give the student 

 adequate help in testing his own factual knowledge and his own 

 organizing ability. Self-testing devices are useful toward this 

 end. All of the units included in the text have such devices. 

 Formal summaries are purposely omitted. Instead, outline sum- 

 maries, to be completed by the pupil, are used. 



This book follows the approved unit structure, and each unit is 

 built on a general plan which has been tested and found to give 

 satisfactory results. The unit is introduced by a number of survey 

 questions intended to interest the group in the work which follows 

 and to give the teacher an opportunity to find out what " apper- 

 ceptive mass " exists in the minds of the pupils. This device may 



