PREFACE xi 



plan the sequence that best fits the season. In fact, the last 

 use that a good teacher will make of any laboratory manual 

 or text-book is that of following it slavishly. It is the hope 

 of the authors, however, that the laboratory guides and the 

 text descriptions which follow may be sufficiently sugges- 

 tive to help some teachers to work out improved methods 

 in biological instruction. In Appendix II will be found a 

 suggested order of topics which the authors have found 

 satisfactory. 



Living organisms are to a large extent to be regarded as 

 chemical engines so constructed as to liberate different kinds 

 of energy. No one, of course, knows in any ultimate sense 

 how even the simplest functions are performed by the sim- 

 plest animals or plants. But it is utterly useless to attempt 

 to teach biological functions without first presenting some of 

 the elementary principles involved in physical and chemical 

 phenomena. For this reason the first chapter in Plant 

 Biology is devoted to the study of the Composition of Lifeless 

 and Living Things. In Chapter III is a brief discussion of 

 the structure of a common plant, and since cells are funda- 

 mentally alike in structure and functions in all living or- 

 ganisms, emphasis is laid early in the course on the essential 

 characteristics of these cellular elements in plants. Another 

 topic which necessarily recurs throughout plant, animal, and 

 human biology is the principle of osmosis and its applica- 

 tions. The authors have inserted experiments which in their 

 experience have helped to fix in mind this important principle 

 and which demonstrate the necessity of digestion in plants 

 and animals. 



After this brief consideration of the fundamentals of plant 

 composition, structure, and processes, Chapters V, VI, and 

 VII are devoted to the study of the adaptations of plants 

 for performing nutritive and reproductive functions. In 



