In all the species of Fagonia, and in the two species of Zygophyllum in Dr. Oudney’s collection, a character in the fructification still remains, which is not found in Diosmeæ or Rutaceæ, and which, were it general in Zygophylleæ, would satisfactorily distinguish this order from all the families it has usually been compared with. This character consists in the direction of the embryo with relation to the insertion of the funiculus, its radicle being seated at the opposite extremity of the seed, or to express, in the unimpregnated ovarium, the infallible indication of this position, the direction of the inner membrane and nucleus of the ovulum corresponds with that of its testa.
But this character, in general very uniform in natural families, and which, equally existing in Cistineæ, so well defines the limits of that order, as I have long since remarked[102], would seem to be of less importance in Zygophylleæ.
M. Adrien de Jussieu, who, in his memoir already cited, admits its existence in Fagonia, and in both our species of Zygophyllum, considers it as an exception to the general structure of the latter genus, in the definition of which he retains the character of “radicula hilo proxima.” I believe, however, that in all the species of Zygophyllum, except Fabago, which possesses, also, other distinguishing characters, this opposition of the radicle to the external hilum will be found; for in addition to the two species contained in the herbarium, in both of which it is very manifest, I have observed it in Z. coccineum, and in all the species of South Africa that I have had an opportunity of examining. In some of these species, indeed, it is much less obvious, partly from the greater breadth of the funiculus, and also from its being closely applied, or even slightly adhering, to the testa of the seed. But hence it is possible to reconcile the structure of these species with that of Fabago itself, in which the raphe seems to me to be external: and if this be really the case, Fabago differs from those Zygophylla of South Africa alluded to, merely in the more intimate union of the funiculus with the surface of the testa. Whether this observation might be extended to the other genera of the order, I have not yet attempted to ascertain.
Balanites Ægyptiaca, though not belonging to Zygophylleæ, may be here mentioned. The specimen is from Bornou, but like all the other plants of that country, has no particular place of growth indicated, nor is there any observation respecting it. For a very full and interesting history of this plant, I may refer to M. Delile’s Flore d’Egypte (p. 77. tab. 28).
Of Cistineæ, three species were observed between Tripoli and Mourzuk.
The Geraniaceæ of the collection consist of four species of Erodium, all of which were found on the same journey.
Of Malvaceæ, considered as a class, there are twelve species in the herbarium. Only two of these are particularly deserving of notice. The first, Adansonia digitata, found in Soudan, where the tree is called Kouka, is described by Captain Clapperton; the second, Melhania Denhamii, a new and remarkable species of the genus, differing from all the others in having its bracteæ regularly verticillated, and, at the same time, longer and much broader than the divisions of the calyx.
A single species of Vitis is in the collection, from Bornou.
Neurada prostrata, generally referred to Rosaceæ, was found in Wady Ghrurbi.
Tamariscineæ. A species of Tamarix, apparently not different from T. gallica, is the Attil, common in Fezzan, where, according to Dr. Oudney, it is the only shady tree.