PREFACE TO THE SECOND EDITION 



During the past five years since the first edition of this book 

 appeared, it has met with more favor in the eyes of teachers and 

 students of the subject than the author (or the publishers) had 

 anticipated even in the most sanguine moments. But during those 

 five years much phytophysiological water has passed under the 

 botanical bridge. Once again has come the task of deciding what 

 matter shall be included and what shall not. There is also the 

 question of maintaining the book within a reasonable size. No 

 self-respecting student can be expected to carry an " elementary' 1 

 book of more than 500 pages. Most gospels are small; but revisions 

 have a tendency to get bigger and (let us hope) better. 



An elementary text should be "up to date" and yet not con- 

 tain many disputable data. However, if one included in a text- 

 book only those facts to which every plant physiologist subscribed 

 wholeheartedly all of the time, the author would finish with a mere 

 pamphlet. A happy medium must be sought. Whether the teacher- 

 professor who reads this will think this golden mean has here been 

 attained, will depend upon his personal predilections and the 

 number of fields in which he is not a specialist. 



So in this, as in the previous edition, there has been an attempt 

 to hold as much as possible to the essentials of a general, elementary 

 course, bearing in mind that this elementary course may be pre- 

 paring the student for courses in horticulture, agronomy, or 

 forestry; for more advanced courses in plant physiology; or for 

 a more appreciative life in the nonprofessional world. 



This edition, therefore, presents no radical changes from the 

 first edition. Many of the sections have been enlarged, and in 

 some chapters new sections have been added, where further ex- 

 pansion seemed warranted by advances in those particular fields. 

 New references, of course, have been included; the selections are 

 varied and should appeal to many types of student-readers. The 

 order of presentation is essentially unchanged. There are some 

 who think that, because the plant absorbs water before it begins 

 making carbohydrates, absorption should be treated before photo- 

 synthesis, or that, because "in actual life probably all respiration 



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