viii PREFACE 



we have just referred. In doing this, they are conscious 

 that many subjects have been slighted or altogether omitted 

 which might well be treated in a year's work in either botany, 

 or zoology, or human physiology. 



Again, in the treatment of a given subject, for example, 

 stems, fishes, or circulation, special emphasis might be laid 

 on structure, on function, or on the relation of the given topic 

 to human life. Books both interesting and scientifically 

 worth while could be prepared along any one of these lines, 

 or, if time permitted, all three phases might be equally em- 

 phasized. But when we remember that less than two hun- 

 dred school periods will probably be devoted by the average 

 student to the study of biology, the necessity for adhering 

 pretty consistently to some one plan is obvious. 



In the judgment of the authors the kind of biology most 

 worth while for the average boy or girl of fourteen years 

 of age is not one based primarily on structure. Young stu- 

 dents are naturally more interested in activities or func- 

 tions than they are in mere form or structure. Hence, if we 

 wish to work with, rather than " against the grain," we must 

 put function in the foreground of our discussion. Every boy 

 and girl knows, too, that both plants and animals as well as 

 human beings must have food and drink, and that they grow 

 and reproduce their kind. It is relatively much easier, 

 therefore, to unify a course like this along physiological lines 

 than on the basis of morphology, or of homologies of structure, 

 many of which are far too complicated to be made clear to 

 young students. 



If properly outlined and presented, there is probably no 



subject in the school curriculum that can be made of more 



j service to a growing youth than can biology. Biological 



problems confront him at every turn, and if he is a normal 



being, he will have asked himself question after question 



