326 MR. F. N. WILLIAMS: REVISION 
EXPLANATION OF PLATE 19. 
Fig. 1. Nitella dictyosperma, H. & J. Groves. Natural size. 
» » Branchlet of young fruiting whorl. Magnified. 
» n Fruiting node of do. x 30. 
Plates of antheridium. x 60. 
» » Young fruit. x 140. 
» » Coronula. X 140. 
» » Nearly ripe fruit. x 60. 
» » Oospore, front view. x 60. 
The same, side view. x 60. 
» » Surfaee of oospore. x 425. From a photo- 
micrograph kindly taken for us by Mr. J. 
Guardia. 
TTS oe yf 
_ 
So @ 
1. » » Apices of ultimate rays, young. X 60. 
1 » » The same, older. x 60. 
A Revision of the genus ARENARTA, Linn. 
By Freperic N. Wirus, F.L.S. 
[Read 17th February, 1898.] 
I. INTRODUCTION. 
Tue first reference to Arenaria as the name of a genus is by 
Jean Bauhin*, who refers to it a plant sent to him by Sprenger 
from the neighbourhood of Ulm in Würtemberg; but the plant 
therein figured, and afterwards more fully described under the 
name of ‘Arenaria : Holostei forte genus’ by Dominique Chabreyt, 
is the species now known as Sagina nodosa, Fenzl. . 
The genus Arenaria was defined and circumscribed by Liu- 
næus T in the following terms :— 
* Calyx. Perianthium 5-phyllum : foliolis oblongis, acuminatis, 
persistentibus. 
Corolla. Petala 5, ovata, calyce ferme breviora, marce 
centia. 
Stamina. Filamenta 10, subulata, alterna interiora. Antheræ 
subrotundæ. 
* ‘Historia Plantarum Universalis, iii. p- 723 (1651). pa 
t * Omnium Stirpium Sciagraphia et Icones,” p. 450 (1677). 
t ‘Genera Plantarum,’ ed. I. p. 133, n. 374 (1737). 
