Xll PREFACE 



of life-histories. A successful teacher of zoology once 

 declared that frogs were created for the express purpose 

 of serving as the introductory type in the study of that 

 science; as strong a claim may be made for the fern in 

 botany. 



Such concepts as alternation of generations, sexual vs. 

 asexual reproduction, fertilization, heredity, adjustment 

 to environment, life-cycle' are nowhere more clearly illus- 

 trated than in the fern; the essence of them all may be 

 clearly comprehended by anyone who has carefully studied 

 its life-history. And with what a rich equipment may the 

 life-histories of all other forms, both higher and lower, be 

 then undertaken! As Athene sprang full armed from the 

 imperial head of Zeus, so, from a study of the fern, do all 

 the essentials of alternation, sex, life-cycle, et cetera, leap 

 clearly defined into the mind of the beginning student, 

 there to remain throughout the course, illuminating all 

 subsequent studies of life-histories. 



During the past fifteen or twenty years it has been the 

 general, if not universal, custom to study in the laboratory 

 the same forms as those treated in the text. Part II of 

 the present book has been planned with the idea of having, 

 for the most part, different sets of forms discussed in the 

 laboratory and the lecture room. This plan not only gives 

 the pupil acquaintance with a wider range of types, but 

 also tend to insure greater independence in the laboratory 

 work. It has been tacitly assumed that, in connection 

 with the use of this text, substantially the same classic 

 types will be studied in the laboratory as have formed the 

 basis of laboratory work for two decades. They are not 

 only types for which material may be obtained with com- 

 parative ease in quantity, but also forms which have been 



