Xll PREFACE 



Chapter VIII are grouped experiments and descriptions 

 the aim of which is to show various ways in which plants 

 are propagated. This treatment presents only the briefest 

 statement of underlying principles, since any extended dis- 

 cussion of this topic belongs to a course in agriculture. 



In Chapters IX (Plants in their Relation to Human Wel- 

 fare) and X (Plant Classification) the method of presentation 

 is strikingly different from that adopted in the rest of the 

 book, particularly so in the treatment of the spore-bearing 

 plants. The authors believe that every pupil should be 

 taught something of these simpler forms (especially bacteria), 

 and that he should get as many of these facts as possible by 

 observation. But to expect much laboratory work from young 

 students on difficult microscopic forms like many of these 

 cryptogams, is, we are confident, quite out of the question. 

 We have, therefore, frankly abandoned the inductive method 

 of study and have suggested that the laboratory work be 

 largely in the nature of demonstrations. It is, of course, 

 understood that if these forms are studied, the drawings and 

 descriptions will be prepared from material in the hands of 

 the student. 



In our judgment there are few if any biological topics 

 which are more important in their practical bearings than is 

 that of bacteria. As commonly studied the disease-pro- 

 ducing effects of these organisms are emphasized so much that 

 boys and girls do not appreciate that all the work of the 

 higher plants depends ultimately upon the activity of these 

 low forms of fungi. In order to bring out this aspect of the 

 work of bacteria and for other obvious reasons the structure, 

 physiology, and economic benefit of these organisms are con- 

 sidered in the chapter on the relation of plants .to human 

 welfare, while their pathogenic effects are reserved for dis- 

 cussion in human biology. 



