26 MEMOIRS FEOM THE DEPARTMENT OF BOTANY OF COLUMBIA UNIVERSITY 



mens in most species 20 in three series, in P. siilphurea 30, in P. staminea 40. The pubes- 

 cence and form of the leaflets is very variable. 



The group differs from Aureae, Gondnnae, and Subviscosae, mainly in the size of the 

 plants ; from Argenteae in the less leafy stem and larger flowers, and from Haematochn in 

 the color of the petals. 



This group is the most difficult in the whole genus. It contains so many and so per- 

 plexing forms, that I have not yet. come to any satisfactory conclusion as to how to treat 

 it. Watson united all species of the United States (except P. pulcherrima and P. sulphurea) 

 into one species. This is far from satisfactory; it would have been much more logical 

 to make P. effusa a variety of P. Hippiana, P. Brewer i one of P. Plattensis or P. emargi- 

 nata one of P. fragiformis than to include P. KuttalHi and P. flabelliformis in P. gracilis. 

 The group contains not less than eleven well marked North American forms and about 

 half a dozen less marked. Of these forms all except two have been recognized at one time 

 or another as species or varieties, and as far as I know, all but one have received names. 

 I shall temporarily regard these eleven as species. 



This view I venture to express, as I have had opportunity to study the group espe- 

 cially in the field. I have collected the following : P. jJulcherrima, Blaschlceana, flabelli- 

 formis, denophora, fastigiata, etomentosa and Nuttallii. I have seen the following grow- 

 ing together : pulchemma and Nuttallii, Blaschkeana and Nuttallii, Blaschlceana and flabel- 

 liformis, Blaschlceana and cfenopAora, flabelliformis and Nuttallii. In no case have I found 

 intermediate forms. In the herbaria that I have looked over I have found one specimen 

 between Blaschkeana and ctenophora, and a few between Nuttallii and Blaschkeana or fasti- 

 giata, but as a rule they can be distinguished fairly well. (Taller forms of P. dissecta 

 will be sought in this group.) 



Leaflets merely crenate or serrate. 

 Leaves green on both sides. 



Leaves thick and leathery ; stem glandular above. 39. p. subcoriacea. 



Leaves thin. 



Leaflets crenate ; petals little exceediug the sepals. 40. P. etomentosa. 



Leaflets coarsely serrate. 



Basal leaves 7-foliolate ; petals twice as long as the sepals. 41. P. heptaphylla. 



Basal leaves 5-foliolate ; petals not twice as long as the sepals. [35. P. dissecta.] 

 Leaves grayish-silky and slightly tomentulose beneath ; plant rather low. 42. P. fastigiata. 



Leaves densely tomentose beneath. 



Stem sparingly silky-strigose, slender. 43_ p p^i^herrima. 



Stem and petioles rather densely villous with spreading hairs (Mexican). 



Stem 4-6 dm. high, leafy ; basal leaves 7-foUolate. 44. p staminea. 



Stem less than 3 dm. high, 1-2-leaved ; basal leaves 5-foliolate. 45. p. leptopetala. 



