4 MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA UNIVERSITY. 
trum by Schur.t As the group has no representative in America, except, perhaps, dP: 
ovalis of Mexico, I have not made any attempt to investigate the validity of the genus. 
Sprengel? suggests that a genus Trichothalanus ought perhaps to be made of the Po- 
tentillae, which have a long-hairy receptacle, and ends his list with P. tridentata. As 
the other species enumerated have terminal styles and are herbaceous, and Lehmann’ has 
taken up Trichothalamus as a generic name for P. lignosa, it is not available for P. triden- 
tutu. Trichothalamus Lehm. was changed to Lehmannia by Trattinnick.’ 
Bigelow’ proposed the genus Bootia for P. arguta. In my opinion that species, to- 
gether with about a dozen others, represents a genus quite distinet from Potentilla, but, 
unfortunately, Bootia of Bigelow is antedated by Boottia of Necker. 
Chamisso during his collecting in California found a plant, nearly related to Poten- 
tilla, but apparently distinct enough to constitute a genus by itself. It was described by 
him and Schlechtendal in Linnaea® under the name Horkelia Californica. The genus 
was merged into Sibbaldia by Sprengel‘ but soon taken out again. It has generally been 
regarded as a good genus by American botanists. 
Thirty years later Torre 
y and Gray* found that H. Gordonii and another undescribed 
species lacked some of the essential characters of Horkelia, being intermediate between 
it and Potentilla and Sibbaldia, and established the genus Ivesia. As the number of dis- 
covered species increased, the generic lines between these four genera became more and 
more indistinct, especially as three good Potentillae were described and kept in Jvesia, 
for what reason, I do not know. This led Bentham and Hooker’ to unite Potentilla, 
Horkelia, Ivesia and Comarum in one genus. This treatment was followed by Baillon” 
and by Greene.” 
Tourreau ” published in 1868 a catalogue of the plants that grow spontaneously 
along the course of the Rhone, and, in this catalogue, he divided Potentilla (Sibbaldia 
and Comarum excluded) into eight genera, viz., Fraga, Trichothalanvus, Dynamidiun, 
Tormentilla, Chamaephyton, Drymocallis, Hypargyrium and Potentilla. He gave no de- 
scriptions nor any reason for the division, but merely cited the species belonging to each. 
In Potentilla he had only one species, P. Anserina. As that species was removed from 
Potentilla by Lamarck, we are not obliged to adopt any of Tourreau’s generic names for 
the large group of true Pofentillac and rename about 200 species. ‘The only one of his 
1Enum. Pl. Trans. 187. 1866.* 7 Syst. 4: part 2, 341. 1827. 
2 Ani. Kent. d. Gew., Ed. 2, 2: 864. 1818. 8 Pac. R. Rep. 6: 72. 1857. 
3 Noy. Act. Nat. Cur. 10: 585. 1821.* °Gen. Plant, 1: 621. 1867. 
4Ros. Mon. 4: 144. 1824.* 10 Hist. de Plantes, 1: 369. 1869. 
5 Fl. Bost. Ed. 2, 351. 1824. 1 Pittonia, 1: 95. 1887. 
62: 26. 1827. 12 Ann. Soe. Linn. Lyon, (II) 16: 302-404. 1868. 
