APRIL, 1919. XANTHIUM MILLSPAUGH AND SHERFF. 13 



Fructus minores : 



Fructi maturi subvirides 2. X. stramarium 



Fructi maturi plerumque flavidi aut rubri: 

 Fructus corpus anguste cylindricum: 

 Aculei recti ad apicem hamosi 8. X. leptocarpum 



Aculei dimidio supero flexi 7. X. curvescens 



Fructus corpus ovatum aut oblongum: 

 Aculei cartilaginei, crassi, fructus cor- 



pore tire. 8 mm. crasso 13. X. calvum 



Aculei subtenues, fructus corpore pler- 

 umque 5-6 mm. crasso 9. X. Wootoni 

 Aculei plures: 



Fructi glabri aut subglabri: 

 Fructus corpus plerumque cylindricum: 



Folia acute lobata; fructibus venustis; aculeis tenuibus, 

 2 -5~3-5 mm - longis 4. X. cylindricum 



Folia subobtuse lobata; fructibus crassioribus; aculeis 

 crassioribus et saepius 3.5-7 mm. longis 



12. X. pennsylvanicum 

 Fructus corpus plerumque crasso-ovoideum aut subglo- 



bosum: 



Rostra elongata (6-9 mm. longa); species mexicana et 

 austro-americana 15. X. australe 



Rostra non elongata (3-4 mm. longa); 



species boralior 5. X. globosum 



Fructus corpus ovato-oblongum: 

 Aculei breves (saepius tire. 2 mm. longi), 



basi dilatati 14. X. palustre 



Aculei longiores, basi non perspicue dilatati: 

 Rostra brevia (circ. 2 mm. longa), crassa 



2. X. strumarium 



Rostra longiora (3-6 mm. longa), tenuiora: 

 Aculei conf erti, arcuati : 



Quidam aculei ad fructus rostra longissimi (8-10 



mm.) ; rostris 5-7 mm. longis n. X. inflexum 



Aculei aequales aut subaequales (4-6 mm. longis) ; 



rostris 3.5-5 mm. longis 6. X. arcuatum 



Aculei remotiores, recti 3. X.' chinense 



Fructus plus minusve setosi, hispidi aut pilosi: 



Aculei fructuum maturorum dense, longe et molliter fusco- 



pilosi 1 8. X. acerosum 



Aculei fructuum maturorum setosi aut hispidi sed non vere 



longo- et molli-pilosi : 



Fructus 8-1 2 mm. longi ; aculeis tircum 2 mm. longis (specie 

 maximam partem gerontogaea) 2. X. strumarium 

 Fructus et aculei longiores : 

 Aculei valde hispidi: 



Corporis latitude quam longitudo 



circ. dimidio minor 16. X. echinatum 



Corporis latitude etiam minor 17. X. italicum 



