SiLENALES.] SILENALES. 495 



Alliance XXXVII. SILENALES.— Tse Silenal Alliance. 



Diagnosis. — Hypogynous Exogens, with monodichlamydeous flowers, a free central pla- 

 centa, an external embryo curved round a little mealy albumen, and more than one 

 carpel completely combined into a compound fruit. 



At this point a considerable advance in structure is evident among Exogens. Among 

 these plants a corolla appears with all its fragrance and gaudy colours, and the ovary is 

 constituted, not by the roUing up of a soUtary carpellary leaf, but by the complete conso- 

 lidation of several. The combiaing process is indeed carried occasionally so fai' among 

 these plants as to divide the cavity of the ovary into distinct cells ; but it is certain that 

 the placentation is in all cases strictly central, no power being possessed by the carpel- 

 lary leaves of generating ovules on their margin or sides. 



The Buckwheat Order (Polygonacese) estabhshes a transition from the Chenopodals, 

 by \Trtue of its uniform want of corolla ; another passage is supphed by Knotworts 

 (lUecebraceee), which are only Amaranths of a higher grade. In both these Orders the 

 ovary may seem to be in many instances as simple as in the Chenopodal AUiance ; but 

 its compound nature is brought into evidence by the number of its separate stigmas or 

 by the manner in which the seed-vessel spUts when ripe. 



Natural Orders of Silenals. 



Calyx and corolla usually both present and symmetrical (4 and ] 



4, or 5 and 5), the latter conspicuous. Ovules amphitropal. 1-188. Caryophyllace-e. 



Leaves opposite^ without stipules J 



Calyx and corolla usually both present and syminetncal (4 and 1 



4, or 5 and 5), the latter rudimentary. Ovules amphitropal. > 189. Illecebrace^e. 



Leaves with scarious stipules J 



Calyx and corolla both p^^esent and unsymm^trical (2 and 5),1 



the latter usually conspicuous. Ovules amphitropal. Leaves \-\90. Portulacace^. 



alternate, succulent, without stipides J 



Cahjx only present, but often coloured. Ovules orthotropal. Nut 1 , q, t)^^ ^^^„ . ^^ „ 



usually triangular |191. Polygonace^. 



