The points in the structure of Reseda, which appear to have led Mr. Lindley to this hypothesis, are the presence and appearance of the hypogynous disk, the anomalous structure of the petals, and the singular æstivation of the flower; but it is no slight confirmation of the correctness of M. de Jussieu’s opinion, that all these anomalies occur in a greater or less degree in Capparideæ, and have been found united in no other family of plants. The remarkable æstivation of Reseda equally exists in Crateva, and in more than one subdivision of the genus Cleome; the hypogynous disk is developed in as great a degree in several Capparideæ; and an approximation to the same kind of irregularity in the petals occurs in two sections of Cleome.
The analogical argument alone then might, perhaps, be regarded as conclusive against the hypothesis. But the question, as far as relates to the petals, and consequently to the supposed composition of the flower, may be decided still more satisfactorily on other grounds. Both M.M. Tristan and Lindley regard the upper divided membranaceous part of the petal as an appendage to the lower, which is generally fleshy. On the other hand, I consider the anomaly to consist in the thickening, dilatation, and inner process of the lower portion, and that all these deviations from ordinary structure are changes which take place after the original formation of the petal. To establish these points, and consequently to prove that the parts in question are simple petals, and neither made up of two cohering envelopes, as M. Tristan supposes, nor of a calyx and abortive stamina, according to M. Lindley’s hypothesis, I shall describe their gradual development, as I have observed it in the common Mignonette; a plant in which all the anomalies that have led to this hypothesis exist in a very great degree.
The flower-bud of Reseda odorata, when it first becomes visible, has the divisions of its calyx slightly imbricate and entirely enclosing the other parts. In this stage the unguis of each of the two upper petals is extremely short, not broader than the base of the lamina, and is perfectly simple; there being no rudiment of the inner process so remarkable in the fully expanded flower. The lamina at the same period may be termed palmato-pinnatifid, its divisions are all in the same plane, the terminating or middle segment is whitish or opake, and several times longer than the lateral segments, which are semitransparent.
Of the remaining four petals, the two middle are dimidiato-pinnatifid, their lateral segments existing only on the upper side; and the two lower are undivided, being reduced to the middle segment or simple lamina. All the petals are erect, and do not cover the stamina in the slightest degree, either in this or in any other stage. The disk is hardly visible. The Antheræ are longer than their filaments, of a pale-green colour; those on the upper or posterior side of the flower being manifestly larger, and slightly tinged with brown. The Pistillum is very minute and open at the top. In the next stage, the calyx is no longer imbricate, but open: the petals have their segments in nearly the same relative proportions; the interior margin of the unguis is just visible; but the transition from unguis to lamina is still imperceptible; the apex of the former not being broader than the base of the latter. It is unnecessary to follow the development through the more advanced stages of the flower, the facts already stated being, in my opinion, absolutely conclusive as to the real nature of the parts in question: and I may remark, that similar observations on certain genera of Caryophylleæ, especially Dianthus, Lychnis and Silene, clearly establish the analogy between their petals and those of Reseda.
I am aware that it has lately been proposed to include Datisca in Resedaceæ, to which it is nearly similar in the structure of its ovarium, as M. de Jussieu has long since remarked. But this is the only point of resemblance between them; for the calyx of Datisca is certainly adherent, and in most of its other characters it differs widely both from Reseda, and from every other genus yet published. Among the numerous discoveries made by Dr. Horsfield in Java, there is a genus, (Tetrameles nob.) however, manifestly related to Datisca, and remarkable in the regular quaternary division of every part of its diœcious flowers. These two genera form an order very different from every other yet established, and which may be named Datisceæ.
Caryophylleæ. Five species only of this family were collected near Tripoli, none of which are new.
Of Zygophylleæ, six species exist in Dr. Oudney’s herbarium, namely, Tribulus terrestris, found in Bornou; Fagonia cretica, from Tripoli to Benioleed; Fagonia arabica, at Aghedem; Fagonia Oudneyi nob. with Zygophyllum simplex in Fezzan; and Zygophyllum album every where in the desert.
This family, so distinct in habit from Diosmeæ or Rutaceæ, with which it was formerly united, is not easily characterized by any very obvious or constant peculiarities in its parts of fructification.
The distinguishing characters in its vegetation or habit are the leaves being constantly opposite with lateral or intermediate stipulæ, being generally compound, and always destitute of the pellucid glands, which universally exist in true Diosmeæ, though not in all Rutaceæ properly so called.
M. Adrien de Jussieu, in his late very excellent Memoir on the great order or class Rutaceæ, in distinguishing Zygophylleæ from the other subdivisions of that class in which he has included it, depends chiefly on the endocarp, or inner lamina of the pericarp, not separating from the outer lamina or united epicarp and sarcocarp, and on the texture of the albumen. His first section of Zygophylleæ, however, is characterised by the want of albumen; and in his second section I find exceptions to the remaining character, especially in Fagonia Mysorensis, in which the two laminæ of the ripe capsule separate as completely as in Diosmeæ. Another plant, in my opinion referrible to the same order, and which, in memory of a very meritorious African traveller, I have named Seetzenia africana, has in its ripe capsule the epicarp, or united epicarp and sarcocarp, confined to the dorsal carina of each cell, the endocarp being the only membrane existing on the sides, which are exposed long before the bursting of the fruit. The plant in question has indeed many other peculiarities, some of which may, perhaps, be considered sufficient to authorise its separation from the order to which I have referred it; for the æstivation of its calyx is valvular, it has no petals, its five styles are distinct to the base, and the cells of its ovarium appear to me to be monospermous. It completely retains, however, the characters of vegetation on which I chiefly depend in distinguishing Zygophylleæ; and I have no doubt of its being Zygophyllum lanatum of Willdenow[101], by whom it is stated to be a native of Sierra Leone; I suppose, however, on insufficient authority, for the specimens in the Banksian Herbarium, from which I have made my observations, were found in South Africa, near Olifant’s River, by Francis Masson.