(3) l'. V WILLIAMS. OH THE GENUS IRENARIA l.iw. 598 



The genus Arenaria was lirst deflned and circumscribed by Linnsus 1 in 

 the folIowiDg terms: — Calyx. Perîanthium 5-phylhim : foliolis obloDgis, 

 acuminatis, persistentibus. Corolla. Pelala 5, ovata, calyce ferme breviora, 

 marcescentia. Stamina. Filaments 10, subulala, alterna inleriora. Antherae 

 subrotundae. Pistillum. Germen ovatum. Slyli 3, erecto-reflexi. Stigmata 

 crassiuscula. Pericarpium. Capsula ovata, lecla, unilocularis, apice 5-fariam 

 dehiscens. Semina. Plurima, reniformia. 



Linnseus enunierated 25 species, of wliich 11 occur in Uie firsl édition 

 of Species Plantarum. As Godron long a go pointed oui. ULychnisis lo be 

 considered as a genus distinct from Silène, then Alsiite should be consi- 

 dered as distinct from Arenaria; as in each case a primary difTerenti.il 

 character is the number of llie leeth of the capsule in relation with the 

 number of the styles. The présence of a strophiole at the hilum of the 

 seed is a constant character, and important enough to exclude a number 

 of species included by some aulhors in Mœhringia; though tins differen- 

 tial character is not mentioned in the Linnean diagnosis of the genus. 

 Most of the olher proposed gênera frequenlly included under Arenaria, 

 in its comprehensive sensé, are best considered as primary subdivisions 

 of Alsine. The genus Arenaria, in this paper, is defîned more in accor- 

 dance with Fenzl's circumscription of the admilled species, and as pro- 

 pounded by him in Endlichere Genera Plantarum. 



Il is difficult in the species of a genus like Arenaria to sélect constant 

 characters which may seem to define satisfactorily and in a natural man- 

 ner the primary subdivisions of the genus. After examina tion of a large 

 number of spécimens, both in the herbarium and in the living slate, I hâve 

 decided to base the primary subdivisions of the genus on the association 

 of two characters which seem fairly constant, viz ; — the structure of the 

 disk, and the number of teelh formed by dehiscence of the ripe capsule. 

 Tliis latter character isgenerally dépendent on and associated with a deti- 

 nite number of styles, but not invariably. For. though one of the impor- 

 tant generic characters is thaï Lhecapsular leeth are twice the number of 

 the styles, it is found thaï the number of styles sometimes varies in spéci- 

 mens of the same species or even in flowers of the same spécimen, while 

 the capsulai 1 leeth are not so liable to casual variation. In such cases, the 

 furrows on the surface of the ovary, which are présent in many species 

 and which correspond with the usual number of styles, are a innre trust- 

 worthy character. though thèse furrows usually disappear with the dis- 



1 Genera Plantarum. cd. I, p. 133, u. 374 (Leydei), 1737). 



