596 BULLETIN DE L'HERBIER BOISSIER. (4) 



tention of the ovary after fertilization. The structure of the disk is a cha- 

 racter which few bolanists besides Edmond Boissier have noticed in 

 their descriptions of species, and the vérification of this character has 

 entailed a considérable examination of material. Plants belonging to 

 Arenaria are of little horticultural interest, and il is difficult to obtain 

 for examination an extensive séries of living or fresh spécimens. Several 

 species grown in the Herbaceous Ground at Kew, and which have flo- 

 wered in the course of the past summer, have afforded advantages for 

 examining spécimens of différent groups side by side under favorable con- 

 ditions. After due considération of the délimitation of other gênera of 

 Caryophyllacece and of their association into groups, and laking into 

 account geographical distribution and systematic variation as shown in 

 the large or small number of species circumscribed by the more important 

 generic types, 1 propose to define the limits and scope of the genus 

 more in accordance with the views expressed by Fenzl rather than with 

 those of botanisls with a more synlhetic bias. 



No systematic account of the known species of Arenaria has been 

 published, and the conspectus of sections which follows is intended as a 

 first instalment of a memoir on the subject. The undiscriminating list of 

 the species by Persoon \ and thefragmentary and meagre descriptions of 

 those enumerated by Seringe 2 , throw but little light on the affinities of 

 the groups of species; and it is only the painstaking and crilical investi- 

 gations of Fenzl that have advanced in any way our knowledge of this 

 widely distribuled genus. Some objection may be raised to the sinking of 

 Dolophragma Fenzl and Brachystemma Don in Arenaria : but the limi- 

 tation of gênera, in natural groups like the order Caryophyllaceie, requires 

 a co-ordination of primary with secondary characlers in a uniform manner 

 in subordinate groups of gênera, in order to preclude as far as possible 

 the isolation of individual gênera distributed sporadically in the guise of 

 what are called (in some German systematic works) « Mittelgattungen » ; 

 and such that the Connecting links in allied groups of gênera should be 

 in a radiating and peripheral séries, rather than in a linear and dicho- 

 tornous séries. In a large natural order there are always a number of 

 cycles ofaffinily which suggesl groupings of gênera, and the more uni- 

 form in coïncidence their limitation the less excuse there will be for the 

 définition of aberrant types. 



1 Syn. Plant. I, p. 502 (1805). 



2 L>C. Prodr. I, p. 401 (1824;. 



