I first introduced this adhesion of the funiculi to the septum, as a generic character, in distinguishing Petrocallis from Draba. It has since been advantageously employed in the character of Lunaria by M. de Candolle, who, however, supposes this structure of much rarer occurrence in Cruciferæ than it really is. According to my observations, it is neither unfrequent, nor always of generic importance. Thus, I find it to exist in some species only of Arabis, namely A. Turrita, pendula, and canadensis, and hence I did not introduce it into my generic character of Parrya, though I have noticed it in my description of the species.
The principal difference existing between these two species of Koniga is that the cells of the ovarium and silicula of K. maritima are monospermous, while those of libyca are polyspermous, the number being variable, apparently indefinite, but not exceeding six. There are, however, other instances in this family, in which the mere difference between definite and indefinite number of seeds is of specific importance only, as in Draba and Meniocus, in each of which a species exists with dispermous cells; and the objection arising from the apparently still greater difference between unity and indefinite number in the two species of Koniga is removed by a supposed third species or variety of K. maritima, in which two seeds are occasionally produced in each cell. It may even be observed, that from unity to the indefinite number in this case, where the ovula in the different cells are alternate, the transition is perhaps more easy than from the binary to the indefinite, in cases where, as in Alyssum properly so called, the ovula are placed opposite in the different cells, and are in the same cell equidistant from its apex; this symmetry, probably, admitting of addition only by fours.
The next genus of Cruciferæ to be noticed is Farsetia, a fragment of the original species of which is in the collection. There are also several specimens of a plant, found in the desert, supposed to be new, and which, though without flowers, and considerably different in the form of its stigma, I am inclined, from the resemblance in habit, in pubescence, in silicula, in seeds, and especially from the exact similarity in the structure of the septum, to refer to the same genus[93].
As the introduction of the structure of the dissepiment into the generic characters of Cruciferæ is now proposed for the first time, and as I believe that its texture and appearance should always be attended to in constituting genera in this family of plants, I shall here offer a few remarks respecting it.
According to the particular view which I briefly but distinctly published in 1818, and which M. de Candolle first adopted in 1821, of the composition of the pistillum in Cruciferæ[94], the dissepiment in this family is necessarily formed of two lamellæ, derived from the parietes of the fruit. These lamellæ are in many cases easily separable, and where their union is more intimate, their existence is still evident from the want of correspondence, and consequent decussation, of their areolæ. The lamellæ, which are usually very thin and transparent, have their surface divided into areolæ, in different genera of very different forms, some of which may, with sufficient clearness, be described. In many cases no other appearance exists; in some, however, the axis of the septum resembles either a single nerve, or two distinct parallel nerves; and from this axis, whether formed of one or two nerves, tubes having the appearance and ramification of the veins of a leaf, and which generally terminate within the margin, not unfrequently proceed. This is remarkably the case in Farsetia, as I here propose to limit that genus; the central vessels in both its species being closely approximated, so as to form a single cord, extending from the apex to the base of the septum, and the veins being numerous and uncommonly distinct. Approaches more or less manifest to this structure of Farsetia exist in several other genera, as in Parrya, Savignya, and Koniga. But in this last mentioned genus the nerve, which originates, as in all cases, at the apex, hardly extends, even in the polyspermous species, beyond the middle of the septum, and the veins, which are much less distinct, are descendent.
As far as my observations on this subject at present extend, I expect, with great confidence, uniformity in the structure of the septum of strictly natural genera, and in many cases, though certainly not in all, I have found a resemblance in this respect in more extensive groups. Thus Draba, Arabis, and Aubrietia, agree in having amorphous areolæ, bounded by flexuose tubes or lines; while Alyssum, Berteroa, and Fibigia, have narrow linear areolæ, bounded by parallel or slightly arched lines. Capsella bursa differs from Thlaspi and Æthionema, as Draba from Alyssum, and agrees with Lepidium procumbens, Linn. improperly referred to Hutchinsia, and which equally has incumbent cotyledons. Cochlearia differs in like manner from Kernera. And numerous other examples of the same agreement in nearly related plants, and of differences where the usual sources of distinction are less available, might be noticed.
Hesperis nitens of Viviani is sparingly in the herbarium, both in flower and fruit. The seeds, though not ripe, are sufficiently advanced to show that the direction of the cotyledons is in this stage accumbent; and, as I have found in Cruciferæ generally that the ultimate agrees with the early state of cotyledons, I conclude they are likewise accumbent in the ripe seed. The plant is also abundantly different from Hesperis in other respects, and does not appear to be referrible to any genus yet published. This new genus[95] I have dedicated to the memory of Dr. Oudney, who found the present species in many of the wadeys between Tripoli and Mourzuk, and remarks that camels and mules eat it.
Hesperis ramosissima, which is also in the herbarium, was found in Fezzan. This plant differs in aspect from most of the other species of Hesperis, approaching in some points to Malcomia, in others to Mathiola; and as its cotyledons are very obliquely incumbent, it may form a section or subgenus, with a name, Hesperis (Plagiloba) ramosissima, indicating that character.
Capparideæ, of which eight species occur in the collection, is the family next to be noticed. I consider this order as belonging to the same natural class with Cruciferæ; and that this class includes also Resedaceæ, Papaveraceæ, and Fumariaceæ.
M. de Candolle, in defining Capparideæ, appears to regard the ovarium as having in all cases only two placentæ, and therefore formed of two pistilla or carpella. But to this, which is certainly the more usual number, there are many exceptions. These exceptions occur chiefly in the genus Capparis, which, as it is at present constituted, includes species differing from each other in having an ovarium with from two to eight placentæ, and, consequently, composed of an equal number of pistilla. Capparis spinosa is the most decided instance of the increased number of placentæ, and this, as well as some other nearly related species, are also remarkable in having septa subdividing the placentæ, and uniting in the centre of the compound ovarium.