NYCTAGINACE2E. 15 



form a sort of supplementary sacciform pericarp around the fruit, 

 completely closed at the apex. This character is never wanting in 

 the Nyctaginacea, neither is the aforesaid organization of the 

 gvnseceum and the constant direction of the single ovule. The 

 variable characters in this little group serving to distinguish the 

 genera are the mode of inflorescence, the shape and colour of the 

 bracts of the involucre, 1 the form of the perianth, the number of 

 stamens, and the shape of the indusium surrounding the fruit. 



The vegetative organs present also several considerable differences 

 in this group. The Pisonias are trees or shrubs. The Bovgainvitteas 

 are thorny or sarmentose shrubs, while, except Boldoa and Colignonia, 

 which may be frutescent, all the other j^ijctaginacece are annual or 

 perennial herbs. The structure of the stems is frequently similar to 

 that of the Piperaceee, inasmuch as their fibro-vascular system is 

 often double ; one interior, and the other exterior. According to 

 Unger,- the latter is formed in MirabUis b} r fibro-vascular bundles, in- 

 dependent of each other and of the central system, and only here and 

 there connected together by lateral anastomoses. The interior, on 

 the contrary, is simple, and consists of a vascular zone whose fascicles 

 pass into the leaves. Oxybaphus, also studied in the same work 

 presents an analogous structure, and has this character in common 

 with MirabUis, that the wood is traversed by irregularly scattered 

 bundles of generative tissue. These observations have been taken 

 up by several authors, 3 and particularly of late years by Eegnault, 4 

 who has proved that there is in Pisonia fragrans, inside the suberous 

 and herbaceous epidermic layers, a rudimentary liber-zone, formed 

 of scattered fibres, scantily dotted between which are cells rich in 

 crystals. Then comes a generative zone, surrounding, as elsewhere* 

 the wood and the pith ; but both of these contain in their interior 



1 Tn Prodromus the family has been divided 2 Essay on the forms and growth of Dicoty- 



from this character into three tribes : the ledonous stems. 



Mirahileee, which have a calyciform involucre; 3 Llsk, Jahresl. (1S40). — Mabt., Gelenrte 

 the BovgainriUece, in which it is formed of large Anzeig. (1842), 391. — LrNDL., Inirod. to Bot., 

 coloured bracts, and the Boerhaaviece which i. 192; Penn. Cyclop., x. (Boerhaavia) ; Introd., 

 have no involucre. This artificial division has 215, fig. (Pisonia) ; Teg. Kingd., 507.— He:.fe., 

 the inconvenience of separating from each other Microsc. Diet., art. Wood (Pisonia, Boer- 

 such types as Mirabilis, and others as Okenia, haavia). — Schletd., Grv.ndz., 251; in Wiegm. 

 Acleisanthes, Pentacrophys, whose organs of vege- Arch. (1839), 223. — Bisch., Lehrb., ii. 64. — 

 tation and efflorescence are absolutely the same, Cbttegeb, in Bot. Zeit. (1850), 164 (Pisonia). — 

 but which have some larger and others smaller Our., Stem, in Dicof., 26. 

 bracts, but always inserted in the same way. * In Ann. Sc. Fat., ser. 4, xiv. 144, t. 9. 



