1921] 
PAYSON—MONOGRAPH OF THE GENUS LESQUERELLA 131 
were L. arctica and L. globosa in 1814. The first of these was 
described as a species of Alyssum by Hornemann and the second 
as a Vesicaria by Desvaux. Two years later Pursh described a 
third species as Myagrum argenteum. For nearly seventy-five 
years after the first species was described, the new species of 
this genus that were reported from time to time were almost 
without exception assigned to the genus Vesicaria. The first 
treatment of these American plants that pretended to be anything 
more than a mere compilation was published by Dr. Gray in 
1850 in the Boston Journal of Natural History. This synopsis 
included nineteen species and was the outgrowth of the study 
made by Dr. Gray of the collections of F. Lindheimer in Texas. 
The second notable contribution to a knowledge of this group 
was published by Sereno Watson in the Proceedings of the 
American Academy of Arts and Sciences for 1888. Here Wat- 
son recognized thirty-three species and called attention totheir 
generie dissimilarity to the Old World members of the genus 
Vesicaria. He proposed “he name Lesquerella for the American 
forms ‘‘in honor of our venerable and in every way worthy 
paleontologist and bryologist, Leo Lesquereux." This revision 
remains essentially unchanged to-day except for the introduction 
of a number of species unknown to Watson and the incorporation 
of a definite theory of phylogeny. Subsequent to the publica- 
tion of the ‘Synoptical Flora of North America’ in 1895, that 
contained a recapitulation of Watson's earlier work, no treatment 
of the genus as a whole has been attempted. The validity of 
Lesquerella as a generic concept has rarely, if ever, been ques- 
tioned in America, and all recent students of the Cruciferae who 
have published on this group have realized that the American 
plants are not closely related to the European and Asiatic plants. 
The resemblance, although sometimes striking, is evidently 
superficial. Aside from the earlier taxonomic works on Les- 
querella, we are greatly indebted to many recent treatments of 
the species of particular regions that have been published in 
various ‘‘Manuals”’ or “Floras.” 
The Type Species of Lesquerella.—It is becoming increasingly 
evident that taxonomists must base their generic concepts 
definitely on a certain species just as they base their specific 
concepts on a particular specimen. It is recognized that there 
