WATER REQUIREMENT AND ADAPTATION IN 



EQUISETUM 



LOUISE DOSDALL 



University of Minnesota, Minneapolis, Minn. 



I. INTRODUCTION 



A study of the water relations of Equisetum was undertaken 

 to throw light upon the nature of bog xerophytes and the 

 successional relations of Equisetum in the hydrosere and paleosere. 



The functional responses of a plant to the water content of its 

 habitat determine the xerophily of the plant. Usually the im- 

 press of an extreme habitat is recognizable at once in the 

 structure of the plant. This, however, is not always the case. 

 In the group of plants known as bog xerophytes many of the 

 members, while superficially exhibiting xerophytic structures, 

 also show characteristics of hydrophytes, namely, large air- 

 spaces and diaphragms. Moreover, these plants grow in the 

 same habitat with true hydrophytes such as Sagittaria, Ranun- 

 culus, and Caltha (Clements 1907: 168). While the nature of 

 the habitat has been subjected to much investigation, very little 

 inquiry has been made as to the nature of the plants them- 

 selves. The purpose of this experimental study of the water 

 requirements and adaptations of Equisetum was to determine 

 whether this plant is a xerophyte as has been supposed, or 

 whether it is truly a hydrophyte as its habitat suggests. 



The problem was suggested by Dr. F. E. Clements and the 

 work was carried on under his direction. The writer gratefully 

 acknowledges her indebtedness for the many helpful suggestions 

 in carrying out the work. Acknowledgments are also offered 

 Miss Frances Long for the determinations of photosynthate and 

 to Mr. Gorm Loftfield for the night readings on the position of 

 the stomata. 



THE PLANT WORLD, VOL. 22, NO. 1 

 JANUARY, 1919 



