INTRODUCTION 7 



be found in the glossary of any botanical text or in a good 

 dictionary. In distinguishing the species it is sometimes 

 necessary to use measurements, and for this purpose (as well 

 as for giving ranges of altitude) the English units of feet 

 and inches are used. But for very small units millimeters 

 (mm.) are used, because they are more convenient. There 

 is no convenient small measure in the English system, it 

 being necessary to refer to everything in some fraction of 

 an inch. To use the English measures therefore involves the 

 continual use of fractions, which is very undesirable. Con- 

 sistency would seem to demand the uniform use of one sys- 

 tem, but the authors prefer to be practical before being 

 scientifically consistent: hence they use millimeters (1-25 of 

 an inch) for all small measurements (the only measurement 

 necessary for the average man to learn) and inches and feet 

 for all measurements over an inch long or thereabouts. 



The common names, as far as they are known to the 

 authors, are given with their proper Latin equivalents in the 

 tabulated list of species, where the distribution in area and 

 altitude (zonal) is nearly always given. By reference to the 

 accompanying zone map a good idea of the distribution of 

 a species may be obtained. The data here given refer only 

 to New Mexico unless otherwise stated. 



