INTRODUCTION 3 



I was attracted to an investigation of the group 

 partly by its great antiquity and partly because so little 

 was known about it. The scanty information was due 

 to a distant and scattered geographical distribution, 

 coupled with the fact that those likely to be interested 

 could not afford such extensive journeys, or at least 

 could not afford them until they became too old for 

 such strenuous collecting. 



My earlier trips were financed by the Botanical 

 Society of America, with such additions as my own 

 slender purse would allow. The most extensive journey 

 was financed, in large part, by the University of Chicago. 



The first thing in the investigation was necessarily 

 to obtain material, and practically none of it could be 

 sent for. Besides, one who knows his material only in 

 the laboratory or greenhouse is sure to get inadequate 

 and often distorted ideas of his subject. The "norm'' 

 of a plant can be determined only by studying it thor- 

 oughly in its natural surroundings, and consequently I 

 have devoted considerable space to field studies and the 

 collection of material. 



