THE PRINCIPLE OF NUMBER. 27 



cessive pairs.* The following may be taken as illustrative 

 instances. The sepals of Fapaver and Fumaria, the outer 

 stamens of Cruciferce. In Circcea all the whorls are dimerous, 

 in Oleacece the essential organs alone, as also in Finguicida^ 

 Salvia, Veronica, and SaUx diandra. 



The question arises, is this number two an original one, 

 or has it arisen by arresting some parts of a more numei'ous 

 whorl ? It is obviously so with Salvia and other genera of 

 the Lahiatoj, where rudimentary stamens are present. So 

 also with Senehlera dldyma where the two stamens take the 

 place of the four larger ones of other genera of the Criiclfercv. 

 It is probably so with the two imbricate sepals of Poppies, 

 those of P. orieiitale being often increased to three, which 

 seems to be a tendency to revert to a more primitive and 

 higher number. 



With sach plants, however, as Circma, the Ash, and Vero- 

 nica, which have retained opposite leaves, the dimerous 

 whorls may be a primitive condition. This idea is ostensibly 

 supported by the fact that the outer whorls of the flowers 

 are quaternary and not quinary, since, when this is the 

 case, the sepals always issue in pairs fiom the axis, and not 

 simultaneously as do the petals ; but as long as no rudi- 

 mentary organs exist, there is nothing to disprove the idea 

 that in these genera the number of stamens ma}^ not be due 

 to degradation. Indeed, all analogy would lead one to 

 suppose so in most cases, as of Circoia and Veronica: the 

 binary whorls of the former genus, and the quaternary outer 

 and binary inner whorls of the lattei', being presumably due 

 to " symmetrical reduction " from the prevailing quaternai-y 



* Though the antero-posterior sepals of cruciferous flowers arc 

 regarded as the most external, it is really the lateral ones which are 

 first provided with fibro-vascular cords from the complete obloug 

 cylinder in the pedicel, just as in Cleomc (see Fig. 6, p. 32). 



