PREFACE vii 



the catalysis of class discussions. Many have been deliberately chosen to extend 

 the classroom discussion to applications which have not been considered in 

 the text. There are a few to which only hypothetical answers can be given, 

 but questions of this type can often be made most useful in stimulating class 

 discussions. We recommend that each teacher who uses this text should 

 augment these lists with additional questions adapted to the interests and 

 background of his own student group. 



The authors believe that effective teaching in any science not only should 

 lead to the acquisition by the student of the basic facts, principles, and view- 

 points of that science, but also should train the student in the use of that 

 science in the interpretation of natural phenomena. Students should come 

 to think of plant physiology' not as a "subject" but as a useful tool which can 

 be used in the explanation of plant behavior under natural or cultural condi- 

 tions. Frequent exposure to properly selected problems and discussion ques- 

 tions will usually aid the student to use the facts and principles of a science 

 as well as to learn them. 



The manuscript has been read in its entirety by Dr. E. N. Transeau, 

 Dr. H. C. Sampson, and Dr. R. O. Freeland of the Department of Botany 

 of the Ohio State University, and by Dr. P. J. Kramer of the Department 

 of Botany of Duke University. We are much indebted for constructive criti- 

 cism to all these readers. Certain chapters have been critically read by 

 Dr. W. G. France of the Department of Chemistry, the Ohio State Univer- 

 sity, Dr. R. C. Burrell of the Department of Agricultural Chemistry of the 

 Ohio State University, Dr. W. H. Camp of the New York Botanical Garden, 

 and Dr. T. Kerr of the United States Department of Agriculture. To these 

 readers we are also grateful for a number of helpful suggestions. Thanks 

 are also due to Dr. B. W. Wells of the Department of Botany of the Col- 

 lege of Agriculture and Engineering of the University of North Carolina, 

 for critical reading of certain chapters and for advice regarding the prepara- 

 tion of several of the figures. 



With a few exceptions the figures are the work of Mrs. Celeste Taft, 

 whose cooperation has aided considerably in their preparation. Those figures 

 which have been redrawn from other sources as well as photographs which 

 have kindly been furnished by several institutions and individuals have been 

 properly credited in the text. Most of the anatomical drawings of leaves and 

 stems and some others have been made from sections of living, undehydrated 

 tissues. For this reason certain details of the tissue structure as depicted do 

 not agree with frequently published figures of the same or similar tissues which 

 are based on dehydrated and fixed tissue sections. In particular the cell walls 

 of many tissues are shown to be thicker than is commonly indicated in similar 



