OF ARTS AND SCIENCES : MAY 13, 1873. 553 



usually smooth ; receptacle short. — From the Missouri River to New 

 Mexico, and westward to Southern California and the valley of the 

 Columbia. A rather variable species. The stamens opposite to the 

 petals and to the'midvein of the sepals are often wanting wholly or in 

 part. The ovules are amphitropous or nearly orthotropous. 



Var. millegrana. (P. millegrana, Engelm.) Leaves all ternate ; 

 stems erect, or weak and ascending ; achenia often small and light-col 

 ored. 



Var. pentandra. {P. pentandra, Engelm.) Leaves ternate, the 

 lateral leaflets of the lower leaves parted nearly to the base ; stamens 

 5, opposite to the sepals. — Dr. Engelmann collected specimens of 

 this in 1835 near Ft. Gibson, Arkansas. It has not been found since, 

 and seems to be but a form of P. rivalis, the usual outer circle of 10 

 stamens (in pairs opposite to the sepals) being suppressed. 



5. P. supina, L. (P. paradoxa, Nutt.) Stems decumbent at base 

 or erect, often stout, leafy, the rootstock apparently sometimes peren- 

 nial ; pubescence scanty, villous, spreading ; stipules ovate, mostly en- 

 tire ; leaflets 5-11, obovate or oblong, £ — §' long ; cymes loose, leafy ; 

 bractlets and sepals nearly equal ; petals obovate, 2" long, equalling 

 the calyx ; stamens 20 ; receptacle thick ; achenia strongly gibbous by 

 the thickening of the very short pedicel. — From the Lakes to the 

 Saskatchewan and "Oregon" (Nuttall), and southward from the Mis- 

 souri to New Mexico. The gibbosity of the achenium, scarcely ob- 

 servable in the European form, and the only distinguishing mark of 

 P. paradoxa, is found fully as decided in specimens from Siberia, 

 China, and the Himalaya. 



Var. Nicolletii. Slender and seemingly decumbent ; leaflets 

 mostly but three ; inflorescence much elongated, leafy, and falsely race- 

 mose. — Collected by Nicollet at Devil's Lake, Minnesota. 



f f Herbaceous perennials, more or less white-tomentose ; leaflets 

 incisely pinnatitid ; bractlets and sepals nearly equal ; stamens 

 20-25. 



6. P. Pennsylvania, L. Silky-tomentose ; stems erect or decum- 

 bent at base, |-2 C high ; stipules incised ; leaflets 5-9, white-tomen- 

 tose beneath, short-pubescent and greener above, oblong, obtuse, often 

 approximate, the linear segments obtuse or acute, slightly or not at all 

 revolute ; cyme fastigiate but rather open, the pedicels erect ; bractlets 

 as long as the sepals or longer, sometimes a little shorter, obtuse or 



VOL. VIII. 70 



