166 TYPE STUDIES 



Part II of this manual presents a series of type studies fur- 

 nishing an outline of the comparative morphology and life 

 histories of plants, upon which are based systems of classifica- 

 tion and various theories of the evolution of the groups. While 

 botanists are in general agreement on the principal lines of 

 plant evolution and in full accord as to the fact that there has 

 been an evolution, the details of the history of development 

 must always remain speculative problems for the reason that 

 evolutionary processes have been in force since very early geo- 

 logical ages and the records of plant life in former periods, pre- 

 served as fossil remains, are relatively scanty. Consequently, 

 while it is often of great interest to draw or diagram lines of 

 plant evolution indicating relationships of groups, such outlines 

 should generally be considered as provisional attempts to help 

 forward discussion rather than as expressions of final judgment. 



Such a study of comparative morphology as may be framed 

 from the matter presented in Parts I and II forms an excellent 

 foundation for detailed work in plant physiology and the funda- 

 mentals of ecology. Indeed, it may be said to be essential to 

 extended work in these subjects, for a knowledge of structure 

 must always precede a study of functions and life activities. 



When a course in botany is planned to begin with type studies 

 such as may be chosen from Part II, the usual procedure would 

 be to supplement or end the course with the more special exam- 

 ination of the seed plants. These latter studies may be not only 

 morphological and physiological but also ecological, and would 

 involve a selection of such topics and experiments from Parts I 

 and III as seem best suited to the conditions under which the 

 work must be given. 



Note carefully the fact that the order of topics in Part III 

 merely follows that of Part III of the authors' Frinciples of Botany. 

 The teacher must shape the order of treatment for himself, 

 choosing such a sequence as may best meet the seasonal succes- 

 sion of plant forms and of phenomena of plant life out of doors. 



