Mærua rigida. This plant, of which flowering specimens were collected at Aghedem, certainly belongs to Forskal’s genus Mærua, adopted by Vahl and De Candolle; and I believe it to be a species distinct from the three already published. It is very nearly related, however, to a fourth species (M. Senegalensisnob.), of which I received a specimen from M. Desfontaines. M. De Candolle has placed the genus Mærua at the end of Capparideæ, between which and Passifloreæ he considers it intermediate. This view of its relation to these two orders I cannot adopt. To me it appears truly a Capparidea, having very little affinity with Passifloreæ, to which it seems to approach in one point only, namely, the corona of the calyx. But of a similar corona rudiments exist in several other African Capparideæ, and from some of these the genus Mærua is with difficulty distinguished[97].
Resedaceæ. The herbarium contains two species of Reseda. The specimens of one of these are too imperfect to be determined. The other is probably undescribed, though very nearly related to R. suffruticulosa, and undata of Linnæus. This supposed new species (Reseda propinqua) was found near Tripoli by Mr. Ritchie, and between Tripoli and Mourzuk by Dr. Oudney. It is remarkable in having the ungues of all the petals simple; that is, neither dilated, thickened, nor having any process or appendage at the point of union with the trifid lamina, into which they gradually pass. We have here therefore a species of Reseda with petals not different in any respect from those of many other families of plants; and, although this is an exception to their usual structure in the genus, I shall endeavour to show that all the deviations existing, however complex in appearance, are reducible to this more simple state of the organ.
Resedaceæ, consisting ofReseda, divisible into sections or subgenera, andOchradenus, which may perhaps be regarded as only one of these subdivisions, I consider very nearly related to Capparideæ, and as forming part of the same natural class. It differs, in the variable number of the parts of itsfloral envelopes, from the other orders of the class, in which the quaternary or binary division is without exception; and it is especially remarkable in having the ovarium open even in its earliest state. From Cruciferæ and Capparideæ, the two families of the class to which they most nearly approach, Resedaceæ also differ in the apparent relation of the stigmata to the placentæ. The stigmata in this order terminate the lobes of the pistillum, and as these lobes are open sterile portions of the modified leaves, from the union of which in the undivided part I suppose the compound ovarium to originate, they necessarily alternate with the placentæ. I have generally found, however, the upper part of each placenta covered by a fleshy or fungous process, which is connected with the margins of the lobes, and therefore with the stigmata, and is probably essential to the fecundation of the ovula. The singular apparent transposition of the placentæ in Sesamoides of Tournefort, so well described by M. Tristan in his ingenious Memoir on the Affinities of Reseda[98], appears to me necessarily connected with the extreme shortness of the undivided base of the ovarium; for in supposing this base to be elongated, the placentæ would become parietal, and the ovula, which are actually resupinate, would assume the direction usual in the order.
M. De Jussieu, in hisGenera Plantarum, has included Reseda in Capparideæ, and to this determination I believe he still adheres. M. Tristan, in the memoir referred to, is inclined to separate it as a family intermediate between Passifloreæ and Cistineæ, but more nearly approaching to the latter. M. De Candolle, who first distinguished Reseda as an order under the name here adopted, in 1819[99]placed it between Polygaleæ and Droseraceæ, and consequently at no great distance from Capparideæ. He must, since, however, have materially altered his opinion respecting it; for the order Resedaceæ is not included in the first or second part of his Prodromus, and I can find no observation respecting it in these two volumes. It is probable, therefore, that he may either intend to place it near Passifloreæ, as suggested by M. Tristan, or, which is more likely, that he has adopted the hypothesis lately advanced, and ingeniously supported, by Mr. Lindley, respecting its structure and affinities[100].
According to this hypothesis, in Reseda the calyx of authors is an involucrum,its petals neutral flowers, and the disk or nectary becomes the calyx of a fertile floret in the centre: and, as a deduction from this view of its structure, the genus has been placed near Euphorbiaceæ.
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 includeDatiscain 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, (Tetramelesnob.) 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 namedDatisceæ.
Caryophylleæ. Five species only of this family were collected near Tripoli, none of which are new.
OfZygophylleæ, 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 Oudneyinob.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 beingconstantly 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 namedSeetzenia 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.
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).
OfCistineæ, three species were observed between Tripoli and Mourzuk.
TheGeraniaceæof the collection consist of four species ofErodium, all of which were found on the same journey.
OfMalvaceæ, 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 andremarkable 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 ofVitisis 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 theAttil, common in Fezzan, where, according to Dr. Oudney, it is the only shady tree.
Lorantheæ. A species of Loranthus, parasitical on the Acacia nilotica, was observed very commonly from Fezzan to Bornou.
Leguminosæ. Of this class the herbarium contains thirty-three species, among which there are hardly more than two undescribed, and these belonging to a well-established genus.
Of the order or tribeMimoseæonly three species occur, namely, Acacia nilotica, Mimosa Habbas, andInga biglobosa, or a species very nearly related to it. Of this last named plant, I judge merely from ripe fruits adhering to the singular club-shaped receptacle, or axis of the spike. The specimens were collected in Soudan, and belong to a tree of considerable importance to the inhabitants of that country, by whom it is calledDoura. According to Captain Clapperton, “The seeds are roasted as we roast coffee, then bruised, and allowed to ferment in water; when they begin to become putrid, they are well washed and pounded; the powder made into cakes, somewhat in the fashion of our chocolate; they form an excellent sauce for all kinds of food. The farinaceous matter surrounding the seeds is made into a pleasant drink, and they also make it into a sweetmeat.” The Doura of Captain Clapperton is probably not specifically different from the Nitta mentioned by Park, in his First Journey; nor from Inga biglobosa of the Flore d’Oware of M. de Beauvois, according to whom it is the Nety of Senegal; and he also well remarks, that Inga biglobosa, described by Jacquin as a native of Martinico, has probably been introduced into that island by the Negroes, as he himself found it to have been in St. Domingo.
Inga Senegalensis of M. De Candolle (Prodr.2. p. 442) may also belong to the same species.
It is possible, however, that some of the plants here mentioned, though very nearly related to each other, and having all the same remarkable club-shaped spike, may be specifically distinct; for it appears from specimens collectedat Sierra Leone by Professor Afzelius, that two plants having this form of spike are known in that colony; and two species, with similar inflorescence, probably distinct from those of Africa, are described in the manuscript Flora Indica of Dr. Roxburgh. All these plants possess characters fully sufficient to distinguish them from Inga, to which they have hitherto been referred. The new genus which they form, one of the most striking and beautiful in equinoxial Africa, I have namedParkia[103], as a tribute of respect to the memory of the celebrated traveller, by whom the fruit of this genus was observed in his first journey, and who, among other services rendered to botany, ascertained that the plant producing Gum Kino is a species of Pterocarpus[104]. I have formerly endeavoured to distinguish Mimoseæ from Cæsalpineæ, by the valvular æstivation of both its floral envelopes, and by the hypogynous insertion of its stamina. Instances of perigynous insertion of stamina have since been noticed by MM. Kunth and Auguste de St. Hilaire; but no exception has been yet pointed out to the valvular æstivation of their calyx and corolla.Parkia, however, differs from other Mimoseæ not only in its æstivation, which is imbricate, but in the very manifest irregularity of its calyx, and in the inequality of its petals, which, though less obvious, is still observable.
Erythrophleum, another genus indigenous to equinoxial Africa, which I have elsewhere[105]had occasion to notice, and then referred to Cæsalpineæ, more properly belongs to Mimoseæ, although its stamina are perigynous. In this genus, both calyx and corolla are perfectly regular, and their æstivation, if not strictly valvular, is at least not manifestly imbricate, though the flower-buds are neither acute nor angular. In Erythrophleum and Parkia, therefore, exceptions to all the assumed characters of Mimoseæ are found, and there is some approach in both genera to the habit of Cæsalpineæ. It is still possible, however, to distinguish, and it will certainly be expedient to preserve, these two tribes or orders. Abandoning divisions strictly natural, and so extensive as the tribes in question, merely because we may not be able to define them with precision, while it would imply, what is far from being the case, that our analysis of their structure is complete, would, at the same time, be fatal to many natural families of plants at present admitted, and among others to the universally received class to which these tribes belong. No clear character, at least, is pointed out in the late elaborate work of M. De Candolle[106], by which Leguminosæ may be distinguished from Terebintaceæ and Rosaceæ, the orders supposed to be the most nearly related to it. It is possible, however, that such characters, though hitherto overlooked, may really exist; and I shall endeavour to show that Leguminosæ, independent of the important but minute differences in the original structure and developement of its ovulum, may still be distinguished at least from Rosaceæ.
In the character of Polygaleæ, which I published in 1814[107], I marked the relation of the parts of the floral envelopes to the axis of the spike, or to the subtending bractea. I introduced this circumstance chiefly to contrast Polygaleæ with Leguminosæ, and to prove, as I conceived, that Securidaca, which had generally been referred to the latter family, really belonged to the former.
M. de Jussieu, who soon after published a character of Polygaleæ, entirely omitted this consideration, and continued to refer Securidaca to Leguminosæ. M. De Candolle, however, in the first volume of his Prodromus, has adoptedboth the character and limits of Polygaleæ, which I had proposed, though apparently not altogether satisfied with the description he himself has given of the divisions of the calyx and corolla.
The disposition of the parts of the floral envelopes, with reference to the axis of the spike, in Polygaleæ, namely, the fifth segment of the calyx being posterior or superior and the fifth petal anterior or inferior, is the usual relation in families the division of whose flower is quinary. This relation is in some cases inverted; one example of which I have formerly pointed out in Lobeliaceæ[108], as I proposed to limit it, and a similar inversion exists in Leguminosæ. But this class also deviates from the more general arrangement of the parts of the flower with regard to each other. That arrangement consists, as I have long since remarked[109], in the regular alternation of the divisions of the proximate organs of the complete flower. To this arrangement, indeed, many exceptions are well known; and M. De Candolle has given a table of all the possible deviations, but without stating how many of these have actually been observed[110].
In Leguminosæ the deviation from the assumed regular arrangement consists in the single pistillum being placed opposite to the lower or anterior segment of the calyx.
In these two characters, namely, the relation of the calyx and corolla both to the simple pistillum and to the axis of the spike or to the bractea, Leguminosæ differ from Rosaceæ, in which the more usual arrangements are found.
But in those Rosaceæ, in which the pistillum is solitary and placed within the anterior petal, its relation to the axis of the spike is the same as that of Leguminosæ, in which it is within the anterior division of the calyx. And in all families, whether dicotyledonous or monocotyledonous, this, I believe, is uniformly the position of the simple solitary pistillum with regard to the spike or bractea.
The frequent reduction of Pistilla, in plants having the other parts of the flower complete in number, must have been generally remarked. But the order in which these abstractions of pistilla take place, or the relations of the reduced series to the other parts of the flower, have, as far as I know, never yet been particularly attended to. It will probably appear singular, that the observation of these relations in the reduced series of pistilla should have suggested theopinion, that in a complete flower, whose parts are definite, the number of stamina and also of pistilla is equal to that of the divisions of the calyx and corolla united in Dicotyledones, and of both series of the perianthium in Monocotyledones.
This assumed complete number of stamina is actually the prevailing number in Monocotyledones; and though in Dicotyledones less frequent than what may be termed the symmetrical number, or that in which all the series are equal, is still found in decandrous and octandrous genera, and in the greater part of Leguminosæ. The tendency to the production of the complete number, where the symmetrical really exists, is manifested in genera belonging or related to those pentandrous families in which the stamina are opposite to the divisions of the corolla, as by Samolus related to Primulaceæ, and by Bæobotrys, having an analogous relation to Myrsineæ; for in both these genera, five additional imperfect stamina are found alternating with the fertile, and consequently occupying the place of the only stamina existing in most pentandrous families. Indications of this number may also be said to exist in the divisions of the hypogynous disk of many pentandrous orders.
With respect to the Pistilla, the complete number is equally rare in both the primary divisions of phænogamous plants. In Monocotyledones, the symmetrical number is very general, while it is much less frequent in Dicotyledones, in which there is commonly a still farther reduction.
Where the number of Pistilla in Dicotyledones is reduced to two, in a flower in which both calyx and corolla are present and their division quinary, one of these pistilla is placed within a division of the calyx, the other opposite to a petal or segment of the corolla. In other words, the addition to the solitary pistillum, (which is constantly anterior or exterior), is posterior or interior. This is the general position of the component parts of a bilocular ovarium, or an ovarium having two parietal placentæ; and in flowers whose division is quinary, I can recollect no other exceptions to it, than in some genera of Dilleniaceæ.
It is particularly deserving of notice, that the common position of the cells of the bilocular pericarpium with relation to the axis of the spike was well known to Cæsalpinus, who expressly distinguishedCruciferæfrom all other bilocular families by their peculiarity in this respect, the loculi in that family being placed right and left, instead of being anterior and posterior[111].
On the subject of the position of the Pistilla in the other degrees of reduction from the symmetrical number, I shall not at present enter. But in reference to Leguminosæ, I may remark, that it would be of importance to ascertain the position of the Pistilla in the pentagynous Mimosea, stated to have been found in Brazil by M. Auguste de St. Hilaire[112]. Are these Pistilla placed opposite to the divisions of the calyx, as might probably be inferred from the position of the solitary Legumen in this class? Or are we to expect to find them opposite to the petals, which is the more usual relation, and their actual place in Cnestis, though the single ovarium of Connarus, a genus belonging to the same family, is seated within the anterior division of the calyx?
In the very few Leguminosæ in which the division of the flower is quaternary, namely, in certain species of Mimosa, the ovarium is still placed within one of the divisions of the calyx.
As toMoringa, which was originally referred to this class from a mistaken notion of its absolutely belonging to Guilandina, it is surely sufficiently different from all Leguminosæ, not only in its compound unilocular ovarium with three parietal placentæ, but also in its simple unilocular antheræ; and it appears to me to be an insulated genus, or family (Moringeæ), whose place in the natural series has not yet been determined.
Cæsalpineæ. Of this tribe, four species only occur in the collection. One of these isBauhinia rufescensof Lamarck (Illustr.329, f. 2.); another isCassia(Senna)obovata, which, according to Dr. Oudney, grows wild in small quantities in Wady Ghrurbi.
Papilionaceæ. Twenty-six species of this tribe are contained in the herbarium, none of which form new genera, and the only two species that appear to be unpublished belong to Indigofera.
Alhagi Maurorum, orAgoul, is abundant in Fezzan, where it forms excellent food for camels.
Compositæ. Of this class, thirty-six species exist in the collection. The far greater part of these were found in the vicinity of Tripoli and in the Desert. All of them appear to belong to established genera, and very few species are undescribed.
Rubiaceæ. The herbarium contains only six species of this family, fiveof which, belonging to Spermacoce and Hedyotis, were found in Bornou and Soudan; the sixth, a species of Galium, near Tripoli.
OfAsclepiadeæonly three plants occur. One of these is a new species of Oxystelma, exactly resembling in its flowers O. esculentum of India, from which it differs in the form of its leaves, and in that of its fruit[113]. A species of Dœmia was found in the Desert; but the specimens are too imperfect to be ascertained.
OfApocineæ, strictly so called, there is no plant whatever in the collection; and of Gentianeæ, a single species only of Erythræa.
Sesameæ. An imperfect specimen ofSesamum pterospermum, of the catalogue of Mr. Salt’s Abyssinian plants[114], is in the collection from Bornou.
Sapoteæ. The only plant of this family in the herbarium is theMicadania, or Butter Tree of Soudan, particularly noticed by Captain Clapperton. The specimen, however, is very imperfect, consisting of detached leaves, an incomplete fruit, and a single ripe seed. On comparing these leaves with the specimen of Park’s Shea Tree[115], in the Banksian Herbarium, I have little doubt that they both belong to one and the same species. Whether this plant is really a Bassia, is not equally certain; and the seed at least agrees better with Vitellaria paradoxa of the younger Gærtner, (Carpol. tab.205.) than with that of Bassia, figured by his father, (de Fruct. et Sem. Pl. tab.104.)
That the woody shell in the nuts of all Sapoteæ is really formed of the testa or outer membrane of the seed, as I have elsewhere stated[116], and not of a portion of the substance of the pericarpium, according to the late M. Richard and the younger Gærtner, is proved not only by the aperture or micropyle being still visible on its surface, as M. Turpin has already shown in one case, (Ann. du Mus. d’Hist. Nat.7,tab.11, f. 3.); but also by the course and termination of the raphe, as exhibited in the younger Gærtner’s figures of Calvaria and Sideroxylum, (Carpol. tabb.200, 201, et 202.) and by the origin and ramification of the internal vessels.
Scrophularinæ. Only six species of this family occur, none of which are unpublished.
Orobanche compactaof Viviani was observed between Fezzan and Bornou.
OfConvolvulaceæthere are five species, four of which belong to Bornou; the fifth is an aquatic Ipomœa, found creeping on the borders of a small lake near Tintuma. Possibly this plant may be Ipomœa aquatica of Forskal, and consequently Convolvulus repens of Vahl, (symb.1, p. 17.) It is not, however, the plant so called by Linnæus, which proves, as I have elsewhere stated, (Prodr. Fl. Nov. Holl.1, p. 483.) to be Calystegia sepium; nor does it belong to either of his synonymes. Our plant differs also from Vahl’s description of his Convolvulus repens, in having constantly single-flowered peduncles, and leaves whose posterior lobes are rather acute than obtuse, and are quite entire. It is probably, therefore, distinct; and I have named it Ipomœa Clappertoni[117].
Among the fewLabiatæ, there is a species of Lavandula, possibly distinct from but very nearly related to L. multifida. It was found on the mountains of Tarhona.
OfBoragineæ, the herbarium includes eleven species, the greater part of which were collected near Tripoli, and all of them belong to well established genera.
Primulaceæ. Of this family two species of Anagallis occur in the collection, and of these A. cærulea was observed both near Tripoli and in Bornou.
Samolus Valerandiwas also found near Tripoli, in Wady Sardalis in Fezzan, and in Bornou.
Of Dicotyledonous, or even of all phænogamous plants,S. valerandiis perhaps the most widely diffused. It is a very general plant in Europe, has been found in several parts of North Africa, in Dr. Oudney’s herbarium it is from Bornou, I have myself observed it at the Cape of Good Hope and in New South Wales, and it is also indigenous to North America.
The geographical distribution of the genus Samolus is equally remarkable. At present eight species are known, of which S. Valerandi is the only one indigenousto Europe, or which, indeed, has been found in the northern hemisphere, except the nearly relatedS. ebracteatusof Cuba. All the other species belong to the southern hemisphere, whereS. Valerandihas also a very extensive range.
OfPlumbagineæ, there are three species ofStatice Taxanthema; for the latter name may be preserved as belonging to a section, though hardly as that of a genus, so far at least as depends on inflorescence, which in both subdivisions of Statice is essentially similar; that ofStatice Armeriabeing only more condensed. Of the three species in the herbarium, one appears to be unpublished.
Among the plants of theApetalous ordersin the collection, there are very few remarkable, and hardly any new species.
Gymnocarpus decandrumwas observed by Dr. Oudney very commonly in gravelly deserts, on the route from Tripoli to Fezzan; andCornulaca monacanthaof M. Delile is said to be widely extended from Tripoli to Bornou, and to be excellent food for camels.
Monocotyledones. The number of species belonging to this primary division contained in the herbarium is altogether seventy. But Gramineæ and Cyperaceæ being excluded, thirteen only remain, namely, three species of Juncus, a single Commelina, three Melanthaceæ, three Asphodeleæ, one species of Iris, and two Aroideæ, of which Pistia Stratiotes is one.
Of these thirteen plants, two appear to be unpublished, both of them belonging to Melanthaceae. The first, a congener of Melanthium punctatum, which is also in the collection, was found in Fezzan.
The second is a species ofColchicum, very different from any hitherto described; and which yet, by Mr. Ritchie, who first observed it, is said to be common in the desert near Tripoli, where it was also found by Dr. Oudney.
This species, which I have namedColchicum Ritchii, is easily distinguished from all its congeners by having two cristæ or membranous processes which are generally fimbriated, at the base of each segment of the perianthium, parallel to each other, and to the intermediate filament. But this character, though excellent as a specific difference, is neither of generic importance, nor sufficient to authorise the formation of a separate section[118].
Bulbocodium and Merendera, however, which, following Mr. Ker[119], I consider as belonging to Colchicum, appear to me decidedly to form subgenera or sections; and in this opinion I am confirmed by having found a fourth section of the same genus. This fourth subgenus is established onHypoxis fascicularis, a plant which has been seen by very few botanists, and which Linnæus introduced into his Species Plantarum, and referred to Hypoxis, solely on the authority of the figure published in Dr. Russell’s History of Aleppo. In the Banksian Herbarium I have examined part of the original specimen of this species, found by Dr. Alexander Russell, and figured by Ehret in the work referred to, as well as more perfect specimens collected by Dr. Patrick Russell; and am satisfied that its ovarium is not in any degree adherent to the tube of the perianthium. I find, also, that Hypoxis fascicularis differs from Colchicum merely in having a simple unilocular ovarium with a single parietal placenta and an undivided style, instead of the compound trilocular ovarium with distinct or partially united styles, common to all the other sections of that genus.
A reduction, as in this case, to the solitary simple pistillum[120], though existing in all Gramineæ and in certain genera of several other families of Monocotyledones, is yet comparatively rare in that primary division of phænogamous plants, and in the great class Liliaceæ, the present species of Colchicum offers, Ibelieve, the only known example. Yet this remarkable character is here so little influential, if I may so speak, that Hypoxis fascicularis very closely resembles some states of Colchicum Ritchii, and in the Banksian herbarium has actually been confounded with another species of the first or trigynous section of the genus.
To the first section, which includesColchicum Ritchii, the subgeneric nameHermodactylummay, perhaps, be applied; while that established on Hypoxis fascicularis may be calledMonocaryum.
The position of the pistillum inColchicum(Monocaryum)fasciculareis not easily determined. I believe it to be placed within the anterior segment of the outer series of the perianthium, but, from the great length of the tube, it is difficult to ascertain such a point in dried specimens. This, however, is the position in which I should expect it, both in reference to the usual relation of the solitary simple pistillum to the axis of the spike, or to the subtending bractea in all phænogamous plants; and also with regard to the constant relation of the parts of the compound pistillum to the divisions of the perianthium in Monocotyledones: for it is worthy of remark, that a difference in this relation may be said to exist in the two primary divisions of phænogamous plants—the pistilla when distinct, or their component parts when united, being in Dicotyledones usually placed opposite to the petals, when these are of equal number; while in Monocotyledones the cells of the trilocular ovarium are, I believe, uniformly opposite to the divisions of the outer series of the perianthium.
Cyperaceæ. Of twelve species of this family existing in the herbarium, six are referrible to Cyperus, three to Fimbristylis, and three to Scirpus. Among these there is no remarkable, nor, I believe, any undescribed species. Of C. Papyrus, which, according to Captain Clapperton, grows in the Shary, there is no specimen in the collection.
Gramineæ. Of this extensive family, with which Dr. Oudney was more conversant than with any other, and to which, therefore, during the expedition, he probably paid greater attention, the herbarium contains forty-five species: and in dividing the order into two great tribes, as I have formerly proposed[121], thirtyof these species belong toPoaceæ, and fifteen toPaniceæ. This relative proportion of these two tribes is considerably different from what might have been expected, in the climates in which the collection was formed: it seems, however, to be connected with the nature of the surface, for in the Great Desert the reduction of Paniceæ is still more remarkable; this tribe being to Poaceæ, in that region, in the proportion of only five to eighteen.
Dr. Oudney remarks with respect to the grasses of the desert, that he observed no species with creeping roots; for a species of Arundo related to Phragmites, which he notices as the only exception, is not properly a desert plant.
Among the very few Gramineæ deserving particular notice, the first isAvena Forskaliiof Vahl. The specimens in the herbarium which were collected in the desert of Tintuma in some respects differ from all the others that I have seen of this variable species. In the Banksian herbarium there is an authentic specimen from Forskal; I have received from M. Delile specimens both of hisA. Forskaliiandarundinacea, described and figured in his Flore d’Egypte; and am also in possession of others in somewhat different states, collected in Egypt by M. Nectoux and Dr. Sieber. From a comparison of all these specimens, I am led to believe, that A. Forskalii and arundinacea are not specifically distinct; and it is at least evident, thatarundinaceamore nearly approaches to the plant of Forskal than that to which M. Delile has applied the nameForskalii.
This grass, which does not belong to Avena, is referrible to Danthonia, from the structure of the outer valve of its perianthium. But Danthonia requires subdivision into several sections, of which, perhaps, our plant may be considered as forming one.
The character of the section established onDanthonia Forskaliiwould chiefly consist in the very remarkable obliquity of the joints of the locusta, which is, indeed, so great, that after their separation each flower seems to have at the base an almost vertically descendent spur; and as the inferior extremity of the upper joint is produced beyond the lower, a short calcar actually exists before separation, and this calcar is equally manifest in the terminal rudiment of the locusta. The present, therefore, is a case of more remarkably oblique articulation in grasses than even that existing inHolcus acicularis(Andropogonacicularis,Retz) which led to the formation ofCentrophorum; a genus still admitted by Professor Sprengel[122], and respecting the structure of which a very singular explanation has been lately offered by M. Raspail[123]. In one respect, the two cases differ. InDanthonia(Centropodia)Forskalii, the articulations being in the axis of the locusta or spicula, each flower appears to have this spur-like process; while inHolcus(Rhaphis)acicularis, the joint being in the peduncle or branch of the racemus, the spur is common to three locustæ.
Dr. Fischer, in whose herbarium the specimen was observed which led to the formation of Centrophorum, will probably recollect the communication made to him on the subject of that plant, of which Dr. Trinius himself has since corrected the characters. He retains it, however, as a distinct genus, for which he has adopted the name Rhaphis, given to it by Loureiro, by whom it was originally proposed, on other, but not more satisfactory grounds.
Triraphis Pumiliois the second plant of this family to be noticed. It is undescribed, and belongs to a genus of which the only two published species were found in the intratropical part of New Holland[124]. In several points of structure the African plant is very different fromT. pungens, the first of these species; in some respects it approaches tomollis, the second species, especially in the inequality of its setæ or aristæ, but it differs from both in habit, and in having only one perfect flower in each locusta[125].
OfPennisetum dichotomum, (Delile, Flore d’Egypte, p. 15, tab. 8, f. 1.), which, in several different states, is in the collection, it is remarked by Dr. Oudney, that “it is a great annoyance to man and beast, from the prickly calyx (involucrum);” and by Major Denham, that from Aghedem to Woodie “it covered the surface of the country, and annoyed the travellers to misery;” he observes, also, that the seed is calledKasheia, and is eaten.
Panicum turgidum, (Forsk. Arab.p. 18;Delile, Flore d’Egypte, p. 19, tab. 19, f. 2.), is also one of the most common grasses from Tripoli to Bornou.
OfAcotyledones, the only plant in the collection isAcrostichum velleum, found on the Tarhona mountains. Mr. Ritchie’s herbarium contains, also, a single plant of the same family, namelyGrammitis Ceterach.
The foregoing observations have extended much beyond the limits which the number and importance of the plants they relate to may seem to require. I still regret, however, that I cannot add a few remarks on such species as, although not in the herbarium, were observed, either indigenous or cultivated, in the countries visited by the mission, and for information respecting which I am indebted to Major Denham and Captain Clapperton. But it being determined no longer to delay the publication of the very interesting Narrative, to which the observations already made will form an Appendix, I am unable at present to enter on this part of my subject.