30 
BOTANY: W. TRELEASE 
PHORADENDRON 
By William Trelease 
DEPARTMENT OF BOTANY. UNIVERSITY OF ILLINOIS 
Presented to the Academy, October 30. 1914 
Several years ago my attention was seriously called to the need of a 
revision of our leafy mistletoes through inability to understand the 
basis of characterization that could admit to one species such different 
appearing plants as those from the southeastern, southwestern, and arid 
United States — not to mention California and Yucatan — to which the 
name Phoradendron flavescens is currently applied Among their mani- 
fold differences, a dihgent search was made for characters; the types of 
related species and varieties that have been held to be differentiable 
from flavescens were examined with care, and every form occurring in 
the United States was traced to the known limits of its range, sometimes 
south of our national border. As political boundaries do not often 
form satisfactory limits to such a study as I had begun, I was quickly 
lured into an examination of the Mexican species which approach our 
border, and of others which reach into the field of these, so that no arbi- 
trary geographical limit, even, could be fixed short of the Isthmus. 
In the course of this study it became apparent that the great conserva- 
tism of Engelmann, who seems never to have given this genus the care 
that marked his study of the related genus Arceuthohium or Razoumofskya, 
had not only caused him to withdraw segregates of P. flavescens that he 
admitted at one time, but had reacted on his early colleague in the study 
of our southwestern plants, Torrey, to the extent of causing a number 
of forms which had been designated in the Torrey herbarium as new 
species to lie there, as they still do, without publication. 
At the New York meeting of the National Academy of Sciences, in 
November, 1911, and at a meeting of the Academy of Science of St. 
Louis on December 18, 1911, the preliminary results of this study of 
the northern species were outlined, and this was followed at the Wash- 
ington meeting of 1912 by presentation to the National Academy of the 
manuscript of a revision of all of the forms of Phoradendron recognized 
as occurring in continental North America. As I was then on the eve 
of departing for a year in the great herbaria of Europe, this revision was 
withheld from immediate publication in the hope that several obscure 
Mexican species could be cleared up certainly, through authentic speci- 
mens, and in the hope that they might be illustrated from the types. 
Though the admission of Torrey's long neglected manuscript names 
