APRIL, 1919. XANTHIUM MILLSPAUGH AND SHERFF. 45 



97447 and 211249; cotypes of X. silphiifolium Greene) ; without locality, 

 in 1879, idem (Hb. Gray); West Klickitat County, bottom lands of the 

 Columbia River, idem 189 (Hb. Gray). ILLINOIS: East St. Louis, 

 banks of the Mississippi River, Sept., 1847, Dr. George Engelmann (Hb. 

 Mo. 85552; form close to X. speciosum Kearney); cultivated by Asa 

 Gray, in botanical garden, Cambridge, Massachusetts, Oct., 1848, from 

 171 and ifia of Dr. George Engelmann, collected presumably in 

 September, 1847, at East St. Louis, 111., with the preceding specimen 

 (2 sheets in Hb. Gray; more typical than Engelmann's own specimen). 



Greene (loc. tit.), in proposing nine species of Xanthium as new, 

 among them X. silphiifolium, laid no claims to a very profound knowl- 

 edge of the genus as a whole. Thus, with reference to Wallroth's mono- 

 graphic treatment of Xanthium, he says: "At present I know nothing 

 as to what his X. laevigatum, pungens, pennsylvanicum, xanthocarpum 

 or oviforme are. Presumably, however, they all belong to the Atlantic 

 slope of the continent. Little or nothing was known of this genus as 

 represented west of the Mississippi in the year 1842 [sic]. As all the 

 following are from far-western regions, I shall, in naming them as new, 

 incur small risk of becoming a manufacturer of synonyms." 



Regarding three of these species, viz. X. pungens, X. pennsylvanicum 

 and"X. xanthocarpum," there need be no doubt as to the forms referred 

 to by Wallroth (cf. pp. 22, 31 and 15). Regarding X. laevigatum, we our- 

 selves are unable as yet to reach positive conclusions. The case of X. 

 oviforme, however, lends itself to very definite treatment. Wallroth's 

 description of this species is decisive and clear. In speaking of the 

 fruits he says (loc. tit.) : "fructibus sessilibus solitariis utrinque aequali- 

 ter rotundatis oviformibus (maximis), aculeis confertis validis corni- 

 formibus basi pilis articulatis ferrugineis densis vestitis cum rostris 

 intus contractis teretibus figura, vestitu et longitudine subconformibus 

 deliquescendo veluti obliteratis." We have also his footnotes regarding 

 the fruits. The first one says: "5) eifo"rmige, in Vergleich zur Pflanze 

 (d.h. dem vorliegenden Probestucke) sehr grosse, mit den Stacheln 

 dem Umfang einer kleinen Wallnuss oder Musskatennuss gleichende 

 Frucht." 1 



1 Two other footnotes in connection with the fruits are given by Wallroth. We 

 reproduce them verbatim herewith: "6) besonders stark ausgebildete, dicht- 

 stehende, 2'" lange Stacheln, welche bis uber die Halfte mit dicht-und abstehenden, 

 gegliederten Haaren umstarrt sind, am oberen Theile aufwarts, in der Mitte etwas 

 abwarts und am Grunde ruckwarts gerichtet sind und den ganzen Fruchtkorper 

 allenthalben dich und gleichmassig umstarren; 



" 7) mit den Stacheln fast gleichformige, nur doppelt so starcke, nach oben rinnen- 

 fdrmig ausgehohlte Stacheln, welche wegen gegenseitiger Aehnlichkeit mit den Sta- 

 cheln gleichsam zu verschwinden oder im Vergleich mit anderen Arten zu fehlen 

 scheinen." The grooved ventral surfaces exhibited by certain of the large basal 

 prickles on the fruits of this species seem indeed an unique character. 



