OF THE GENUS ARENARIA. 331 
South American, and are collectively distinguished from all others 
in the genus by their habit. The leaves are densely crowded in an 
imbricate series on the short stems terminated by small solitary 
flowers; and the seeds are quite smooth, shining and black. In 
the small group of Arenariastrum, the capsule splits by four teeth 
which deepen into valves, containing few seeds. The species of 
the distinctive subgenus Odontostemma have petals eroded or 
laciniate at the margin, and are also characterized by the struc- 
ture of the root. The last subgenus is founded on a species 
from the province of Yunnan described by Mr. A. Franchet*, 
which is remarkable for its long exserted styles and its distinctly 
lobed disk, which is half-free, with a somewhat concave receptacle 
truncate at the base. 
In this Revision of the genus 168 species are admitted, under 
which are also grouped 103 varieties. Of these 168 species, 69 
are represented in the iconography of the genus, and additional 
plates are also cited for 17 varieties. Not many more than a 
third, therefore, of the species have been figured. 
II. GEOGRAPHICAL DISTRIBUTION. 
Arenaria is a genus which includes plants of wide distribution 
both as regards latitude and altitude, chiefly confined to the 
north temperate zone; wituin the Arctic Circle extending beyond 
the limits of permanent human habitations, and in the Tropics 
found only at considerable elevations in mountainous districts. 
Inthe Old World species occur only in the northern hemispheret, 
aud the range of the genus is trom the west coast of Spitzbergen, 
lat. 78° (4. ciliata), to the island of Socotra, lat. 13°(A. serpylli- 
folia), and from the island of Novaya Zemlya (A. ciliata) to the 
Nilehiri Mountains in Malabar, lat. 11? (A. nilghirensis). In 
the Himalayas species are found at considerable altitudes. In 
Capt. Deasy 's recent expedition to North-western Tibet (1896-97), 
Specimens of 4. polytrichoides were gathered at 5800 metres. 
Many years ago specimens of the same species were collected by 
Sir J.D, Hooker in Tibetan Sikkim at 4800 metres, and speci- 
mens of A. pulvinata at 5400 metres, and specimens of A. oreo- 
Phila at nearly as great an elevation in the same region. A. 
densissima was gathered in the Yak Pass by Mr. C. B. Clarke 
* 
; Bull Soc. Bot. France, xxxiii. p. 432 (1886). 
The South-African 4. glandulosa of Jacquin belongs to Spergularia. 
