NYOTAGINACE. 15 
form a sort of supplementary sacciform pericarp around the fruit, 
completely closed at the apex. This character is never wanting in 
the Nyctaginacee, neither is the aforesaid organization of the 
gynæceum 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,' 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 Bougainvilleas 
are thorny or sarmentose shrubs, while, except Boldoa and Colignonia, 
which may be frutescent, all the other Wycfaginacee are annual or 
perennial herbs. The structure of the stems is frequently similar to 
that of the Piperaceæ, inasmuch as their fibro-vascular system is 
often double; one interior, and the other exterior. According to 
Unenr,’ the latter is formed in J/radilis by 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. Ozybaphus, also studied in the same work, 
presents an analogous structure, and has this character in common 
with A/iradilis, that the wood is traversed by irregularly scattered 
bundles of generative tissue. These observations have been taken 
up by several authors,’ and particularly of late years by Regnault,' 
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 In Prodromus the family has been divided ? Essay on the forms and growth of Dicoty- 
from this character into three tribes: the  ledonous stems, 
Mirabilee, which have a calyciform involucre ; 3 Link, Jahresb. (1840).—Marr, Gelehrte 
the Bougainvilleæ, in which it is formed of large Anzeig. (1842), 391.—Linpt., Introd. to Bot., 
coloured bracts, and the Boerhaaviee which i, 192; Penn. Cyclop., x. (Boerhaavia) ; Introd., 
have no involucre. This artificial division has 215, fig. (Pisonia) ; Veg. Kingd., 507.—HENFR., 
the inconvenience of separating from each other Microsc, Dict., art. Wood (Pisonia, Boer- 
such types as Mirabilis, and others as Okenia, haavia).—SonLErD., Grundz., 251; in Wiegm. 
Acleisanthes, Pentacrophys, whose organs ofvege- Arch. (1839), 223.—Biscu., Lehrb., ii, 64,— 
tation and efflorescence are absolutely the same, CRUEGER, in Bot, Zeit. (1850), 164 (Pisonia),— 
but which have some larger and others smaller Orav., Stem. in Dicot., 26. 
bracts, but always inserted in the same way. 4 In Ann, Se, Nat., sér. 4, xiv. 144, t. 9. 
