APRIL, 1919. XANTHIUM MILLSPAUGH AND SHERFF. n 



are some definite but minor differences which might prove of uncertain 

 value in classification." The following year Fair described and illus- 

 trated the origin of the inflorescences of Xanthium (Bot. Gaz. 59: 

 136-148 and pi. 10. 1915). Several interesting conclusions are stated 

 by Fair. Among these, we note (he. cit., p. 145) that the "terminal 

 heads became staminate, because the vascular supply was inadequate 

 to compensate for the excessive transpiration, and hence the pistils 

 have aborted"; also that "the bur is a modified capitulum, differing 

 from the typical head of Compositae chiefly in the two depressions in 

 the receptacle. These pits originate through a temporary arrest of 

 development, which may possibly be attributed to contact with the 

 tips of the recurved involucral bracts. This recurving of the bracts 

 may be the result of limited space due to the subtending structures." 



Throughout the prosecution of our own study, we have received the 

 most generous assistance from other botanists, both in America and 

 in Europe. It is with a sense of genuine pleasure that we express our 

 gratitude for such help, which usually consisted either in loaning 

 herbarium material, in furnishing photographic reproductions of de- 

 scriptions and plates, or in extending to us various herbarium facilities. 

 Chief among those to whom we are thus indebted are Prof. August 

 Be*guinot, Director, R. Orto Botanico, Padua; Dr. Ezra Brainerd of 

 Middlebury, Vermont; Dr. N. L. Britton, Director of the New York 

 Botanical Garden; Miss Mary A. Day, Librarian of Gray Herbarium; 

 the late M. Casimir De Candolle, of Geneva; Mrs. Nellie F. Flynn of 

 Burlington, Vermont; Dr. J. M. Greenman, Curator of the Herbarium 

 of the Missouri Botanical Garden; Dr. H. M. Hall, of the University 

 of California; Professor James M. Macoun, of the Canadian Geological 

 Survey; Mr. Wm. R. Maxon, Associate Curator of the United States 

 National Herbarium; Dr. George T. Moore, Director of the Missouri 

 Botanical Garden; Dr. Julius A. Nieuwland, of the University of Notre 

 Dame (in charge of the Greene Herbarium) ; Sir David Prain, Director 

 of the Royal Botanical Gardens at Kew; Dr. A. B. Rendle, of the 

 British Museum of Natural History; Dr. B. L. Robinson, Curator of 

 Gray Herbarium; Dr. C. A. Shull of the University of Kentucky, and 

 Miss Ethelyn M. Tucker, Librarian of the Arnold Arboretum. 



Upwards of two hundred photographs were made of the more im- 

 portant specimens examined in other herbaria during the progress of 

 the work. These, together with full data, are deposited in the herb- 

 arium of this Museum. 



