iv PREFACE 



petition cultures must also be prepared early in the year. Types 

 of hydrophytes, xerophytes, etc., should be grown in the plant - 

 house in so far as possible. Students should be instructed to make 

 duplicate plantings of all plants to be used in order to make sure 

 of an adequate supply at all times. It has also been found desira- 

 ble to teach the students the use of the paraffin method of em- 

 bedding tissues, thus saving much time and securing better results. 

 The work on adaptation to water and light is best carried on in the 

 form of joint experiments, in which each student is assigned a 

 definite part. In the experiments much use has been made of the 

 common sunflower. This is on account of the ease \A'ith which it 

 may be secured and grown, but when a larger choice is possible 

 other plants may often be substituted to advantage. 



In just as far as possible, the work of the student should be 

 among plants out-of-doors. This is imperative in the chapters on 

 vegetation, and is very desirable in all cases where it is feasible, 

 even in the study of plant functions. For vegetation work, the 

 knowledge of the more important genera and species of the several 

 formations is indispensable. If the student does not already have 

 this knowledge, the names should be furnished him by any desira- 

 ble method, without taking the time necessary for identification. 



A bibliography has not seemed necessary and has not been given. 

 A fairly full list of the more important works is found in "Research 

 INIethods." Apart from the latter, Pfeffer's "Pflanzenphysiologie," 

 MacDougal's "Text-book of Plant Physiology," Sach's "Text-book 

 of Botany," Vines' "Lectures on the Physiology of Plants," and 

 Kerner's " Pflanzenleben " have been frequently consulted in the 

 preparation of the text. 



Grateful acknow^ledgment is made of the kindness of Dr. C. E. 

 Bessey, Dr. D. T. ^lacDougal, and Dr. Edith Clements in reading 

 and criticizing the text. The author is also indebted to Dr. Edith 

 Clements for many drawings, and for the use of cuts from "The 

 Relation of Leaf Structure to Physical Factors," and to Mr. R. J. 

 Pool and Mr. A. W. Sampson for the loan of several photographs. 



Frederic Edward Clements. 

 The University of Nebraska, ^ 

 March 1907. 



