28 MEMOIES PROM THE DEPARTMENT OF BOTANY OF COLUMBIA ITNIVERSITY 



§ 12. FRIGIDAE. 



Plants low with a scaly rootstock, often tufted. Leaves digitately 3-foliolate, not at 

 all tomentose, in ours coarsely toothed. Petals yellow, obcordate. Style filiform, but 

 sometimes short. 



The group is very nearly related to Aureae and Niveae, differing from the former 

 only in the number of the leaflets, and from the latter by the lack of tomentum. (P. 

 Grayi has also 3-foliolate leaves, but the middle leaflet is petiolate, which indicates that 

 the leaves are really pinnate ; as the structure of the pistil is that of P. brevifolia, it is 

 placed in the same group as that species.) 



Leaflets all sessile, or short-petiolate. 



Stem 1-3 dm. liigh, simple ; bractlets oval or elliptic, generally obtuse. 



Leaves smooth. 59. P. flabellifolia. 



Leaves hairy. 



Leaflets broadly obovate, 3-4-crenate at the apex, somewhat glandular. 60. P. Friesiana. 

 Leaflets broadly obovate, coarsely toothed, not glandular. 61. P. fragiformis. 



Stem less than 1 dm. high. 



Petals much exceeding the sepals. 



Teeth of the leaves obtuse, the terminal one smallest. 62. P. nana. 



Teeth of the leaves acute, the terminal one largest. 63. P- emarginata. 



Petals scarcely exceeding the sepals. 64. P. Pobbinsiana. 



Terminal leaflet long-petiolate. rgg. p. Grayi.'] 



§ 13. BIFLORAE. 

 Plant cespitose, the stems subscapose, 1-3-flowered. Leaves ternate with the leaflets 

 divided to near the base into 2 or 3 hnear entire, somewhat revolute segments, not tomen- 

 tose. Petals broadly elliptic, yellow, slightly emarginate. Style long and filiform. Re- 

 ceptacle beset with long hairs. 



The group contains only one species, which shows very little relationship to the 

 others. 



Species. ^.^ t> i-jj 



^ 65. P. bxflora. 



§ 14. NIVEAE. 



Plants mostly low and tufted. Rootstock often thick, scaly. Leaves digitately 3- 

 foliolate, more or less tomentose beneath. Petals obcordate, yellow. Style short, often 

 inchned to be thickened and glandular at the base. 



The relationship of the group is with Goncinnae, Multifidae, and Frigidae. (Trifolio- 

 late specimens of P. quinquefoUa may be sought here.) 



