MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA UNIVERSITY 13 
This explanation seems to me rather unsatisfactory, but Iam unable to give any other 
in its place. Dickson states that he had found the same arrangement in the European 
P. rupestris. I have confirmed Dickson’s observations in both species and find that P. 
fruticosa has the same arrangement of stamens as P. arguta, P. glandulosa and their rela- 
tives, but the thickening of the disk is less prominent. P. rupestris belongs to the same 
group as P. arguta, and all species of that group and P. fruticosa and a few closely 
related Asiatic ones have the same arrangement, but as far as I know it is not found 
elsewhere in the tribe. In the dark red-flowered I otentillae, the disk is somewhat thick- 
ened but the arrangement of the stamens is normal. 
In the two groups with festooned stamens, the anthers are also of different form 
_from those of the rest of the tribe, being flat, searcely at all didymous, oval in outline, 
in some species only slightly cordate at the base, with filaments attached to their backs 
the sacs opening by a slit along the margin. The other species have as a rule anthers 
that are more or less didymous and open by a slit which is more or less on the inside. 
The most remarkable exception is Stellariopsis santolinoides in which the anthers are 
decidedly didymous, each half nearly pear-shaped and opening by a subterminal pore 
( Plate 95). 
In most plants belonging to the tribe the filaments are slender and filiform but in 
Horkelia they are dilated and more or less petaloid ( Plates 56-81). In most they are 
broad, in some even triangular in outline, but in others, as for instance, FH. tridentata 
(Plate 74) and congesta (Plate 76), they are rather narrow and lanceolate. One un- 
described species of the subgenus Lvesta (Plate 84) has also somewhat dilated but narrow 
filaments. 
PISTILS AND FRUIT. 
The ovary is one-ovuled and becomes an achene. In its form there is very little 
variation, at least in the North American species. Nearly all the members of the tribe 
have somewhat obliquely inverted pear-shaped and slightly flattened smooth and elab- 
rous achenes. The only one that in form departs considerably from the usual type is 
Potentilla Anserina in which the achene is much thickened at the upper end, and 
there obtusely triangular in cross-section, and has a very thick and corky shell. In P. 
paradoxa (Plate 5 ) and P. Nicolletii (Plate 6), the achene has a large gibbosity on 
the inner margin. In P. Monspeliensis, P. Canadensis and P. ramulosa the achenes are 
somewhat ribbed and in several others more or less veined. In P. sulphurea they 
are strongly reticulated. In P. fruticosa and P. tridentata they are hairy, in all the 
other species glabrous. 
