APRIL, 1919. XANTHIUM MILLSPATJGH AND SHERFF. 29 



tatum et in duo (aut rarius tria) rostra distantia productum, 12-30 

 aculeis (3.5-6 mm. longis) armatum, molliter glanduloso-pubescens uti 

 bases aculeorum et rostrorum, 1.1-1.4 (rariter 1.6) cm. longum et 5-6 

 (-7, fide Piperi) mm. crassum; rostris rectis aut versus apicem incurva- 

 tis, saepe hiantibus et achaenia in conspectu ponentibus, aculeos 

 aequantibus; aculeis rectis aut subrectis sed ad apicem hamosis, non 

 pubescentibus nisi versus basim. 



DISTRIBUTION : Massachusetts, New Mexico and Washington. 



SPECIMENS EXAMINED: MASSACHUSETTS: South Boston, made land, 

 Oct. 4, 1909, Walter Deane (2 sheets, Hb. Gray). NEW MEXICO: Las 

 Vegas, T. D. A. Cockerell 15 (author's material of X. commune Wootoni 

 Cockerell, Hb. N. Y.); Las Vegas, in 1902, idem (author's material of 

 X. commune Wootoni Cockerell, Hb. Gray). WASHINGTON: Waits- 

 burg, bars of streams, Robt. M. Homer B. 272 (Hb. Gray) ; Bolles, in 

 fields, Sept. 18, 1893, C. V. Piper (Hb. N. Y.; cotype of X. oligacanihum 

 Piper). 



Repeated studies upon this species have indicated it to be distinct 

 and worthy of specific rank. DeVries (loc, tit.} found that the seed sent 

 him by Cockerell (who was the first to pay particular attention to the 

 plant) produced, when planted in DeVries' garden, plants true to type. 

 Wooton and Standley (Contrib. U. S. Nat. Herb. 19: 635. 1915), 

 while reluctantly retaining the form as a variety of Xanihium commune 

 Britton (=X. italicum Moretti), state nevertheless that it "seems 

 distinct enough from X. commune to be regarded as a species. It cer- 

 tainly is more easily separable from that than are most of the eastern 

 species from each other. ..... Ordinarily the two plants are distinct 



enough." Cockerell himself (Science, New Ser. 42: 871. 1915), 

 although at first inclined to regard the plant as a variety, finally, as a 

 result of an additional observation upon X. commune and also in view 

 of DeVries' results, stated, "We must apparently conclude that X. 

 Wootoni is a valid species, but that commune from time to time varies 

 or mutates to a virtually identical form." And, several years before, 

 Piper regarded it as a species. He stated that it differed "from any 

 other American species in the small size of the fruit and the relatively 

 few prickles" (Piper, loc. tit.}. But, as he was dealing with specimens 

 from Washington, he apparently overlooked the literature dealing with 

 X. Wootoni, which had been known only from New Mexico; hence 

 the reason for his name X. oligacanihum. 



We have studied several authentic specimens from New Mexico and 

 from Washington. There is no essential difference to be found between 

 the two sets of specimens. Those from Washington have burs more 

 brownish in color (rather than whitish to straw-colored) and the prickles 

 are very slightly stouter. But both have the beaks of the burs tending 



