PREFACE v 



For the benefit of the teacher and of our professional colleagues, 

 it should be stated that much attention has been given to the avoid- 

 ance of any phraseology that might involve a teleological implication. 

 It has not been possible to avoid such phrases in all cases without 

 introducing clumsiness of expression or breaking the continuity of 

 some important series of structures or events. It should be kept in 

 mind, therefore, that all teleological implications of language that 

 remain are disavowed. 



It seems hardly necessary to say that most of the material presented 

 in the book has been worked over by classes repeatedly. Some new 

 matter has been developed incidentally in all the parts in connection 

 with ordinary laboratory and field work ; and especially in Part III 

 have many scattered observations and some new points of view been, 

 included. There has been no intention to include any formal con- 

 tribution, but merely to present in general outline some of the material 

 worked over by undergraduates, some of the results of investigation 

 already published in 'contributions from the laboratory, and some ob- 

 servations and conclusions that hardly seemed to justify separate pub- 

 lication. Provision has been made for students with more interest 

 or more time than usual to get a somewhat larger view, by including 

 in smaller type further details of structure, additional illustrative 

 material, and suggestive theories. Most of the illustrations are origi- 

 nal, in the sense that they have been prepared especially for this 

 book or have appeared in our own contributions. Those that have 

 been copied or adapted are credited ; the former usually being indi- 

 cated by " from," the latter by " after." 



The three authors are individually responsible only for their own 

 parts, and, while they had the advantage of mutual criticism, it could 

 not be expected that they would agree absolutely at every point. 

 This will explain any lack of harmony that may be discovered in the 

 three parts. A morphologist, a physiologist, and an ecologist look 

 at the same material from different angles, and lay emphasis upon 

 different features ; but all their points of view should be included 

 in any general consideration of plants. It is for this reason, also, 

 that the parts contain a certain amount of repetition, which is abso- 

 lutely necessary when the same structures or functions are being 

 considered from different points of view. 



