A REVISION OF THE AMERICAN SPECIES OF EUPHORBIA OF 
THE SECTION TITHYMALUS OCCURRING NORTH OF MEXICO. 
BY J. B. S. NORTON, 
Since Boissier’s monograph of the genus Euphorbia was 
published in De Candolle’s Prodomus, in 1862, no general 
work on the North American species of the above section 
has appeared, though a number of new species have been dis- 
tinguished, and most of them published in isolated works. 
Before the time of Boissier’s monograph, Dr. George 
Engelmann had done a large amount of work on the genus 
in North America, and published several papers, and had 
at that time a monograph in preparation. Many notes and 
specimens sent by Engelmann were used by Boissier in his 
work. Afterward Dr. Engelmann continued his studies in 
Euphorbia until his death, being the only American botan- 
ist well acquainted with this group of plants. His synop- 
sis of the Euphorbias of the Mexican boundary gives a 
complete account of the species inthe Southwest. In later 
years Dr. C. F. Millspaugh has done considerable work 
upon the genus in this country; but aside from the works 
of Engelmann and Boissier, very little has been published 
upon the section under consideration. 
Some two and a half years ago this revision was begun 
at the Missouri Botanical Garden, and has been carried on 
there with the aid of the Garden herbarium and library, 
which contain the rich and invaluable herbarium, library, 
and notes of Dr. Engelmann. Besides these I have used 
the material of this section from the herbaria of Harvard 
University, Columbia University, the United States 
National Museum, the California Academy of Science, Dr. 
C. F. Millspaugh, the Kansas State Agricultural College, 
1 
Separates issued July 10, 1899. 
