22 FIELD MUSEUM OF NATURAL HISTORY BOTANY, VOL. IV. 



described from Santo Domingo in 1822, under the name X. occidental. 1 

 Moreover it is the same which Wallroth, in 1844, named somewhat 

 provisionally X. longirostre. Wallroth very clearly voiced his hesitancy 

 in publishing a new name, but he had not seen authentic Santo Domingo 

 specimens of X. occidental with which to match his X. longirostre mate- 

 rial from St. Thomas and Haiti, so was constrained not to equate the 

 two names. 



Specimens from the West Indies vary considerably in size of bur and 

 in curvature and length of beaks. Sometimes the prickles are slightly 

 short-hispid near the base, not "simple" as described by Miller. 

 The Greenman plants exhibit this same small departure from the 

 original description. Commonly the burs are rather few, large, in 

 color greenish-brown. A character frequently observed, especially in 

 the West Indian material, is the peculiar appearance of many of the 

 burs, their beaks being long, not widely divergent, somewhat incurved 

 and suggesting the bill of a bird; this character is present on several 

 burs of the Greenman plants. 



Specimens from continental North America usually have the burs 

 more numerous, smaller and more or less reddish in color. These speci- 

 mens harmonize very well with the description of X. pungens Wallr., 

 but the intergradations between the continental and West Indian forms 

 are so numerous as to render vain all our attempts at separation. 1 

 Hence we are compelled to regard X. pungens as merely a form or variety 

 of X. chinense. 



In not a few cases, X. chinense appears from herbarium specimens, to 

 have formed hybrids with X. pennsylvanicum (cj. p. 19, foot-note). At 

 other times the fruits, varying to a coarse, more elongate, more hispid 

 type, display a very close approach to those of the same species, but 

 without suggestion of hybridity. On the whole, however, the two 

 species are very easily distinguishable. 8 



1 Raised from seed sent by Bertero from Santo Domingo. " Nux oblonga, medio 

 ventricosa, utrinque attenuata, muricata, aculeis raris, subulatis, uncinatis, gra- 

 cilibus, apice bi-trirostris, rostris convergentibus, viridis, vix puberula." (Bertol. 

 Lucubr. Herb. 38. 1822). 



* Rydberg (Dr. Per Axel), also Wiegand (Dr. Karl M.) each of whom made a 

 somewhat extended preliminary study of the genus Xanthium and then postponed 

 or abandoned the investigation, appear to have met with the same result. Thus we 

 note on a sheet of typical West Indian material in Gray Herbarium (Brown and 

 Britton 374, Bermuda) the annotation in pencil by Rydberg, "X. americanum 

 P. A. R." and, by Wiegand, "X. pungens Wallr. K. M. W." By X. americanum, 

 Rydberg meant, as his other herbarium annotations show, the X. pungens of Wall- 

 roth, which had of late been referred (by Britton and Brown, Illustr. Fl. Edit. II. 

 3: 346, f. 4139) to the enigmatic X. americanum Walt. 



1 Thellung (Verhandl. Bot. Verein Brandenb. 50: 144. 1908) equates X. 

 pennsylvanicum Wallr., X. occidental Bertol. and various other names categorically 

 with X. echinatum Murr. The chinense of Miller he resolves into two parts, regarding 

 the first or supposedly Chinese form as a variety of X. strumarium L. and referring 



