Abbildungen der Seite
PDF
EPUB

C. africana subspecies winkleri (Forel). Belgian Congo (Kohl; see Forel, 1909, p. 69).

C. africana subspecies winkleri variety fickendeyi (Forel). With regard to this variety Forel (1916, pp. 409-410) writes:

Kohl has collected various forms transitional between the race vrinkteri and the variety fickendeyi, on one occasion in a nest, probably usurped, of Tetramorium aculeatum, also in myrmecophilous plants or in termitaria. His No. 68 bears the following interesting remark: "Ant from plants. Lives in and on the myrmecophyte Plectronia Laurentii De Wildeman. Five meters above the ground the trunk bore a carton nest, 40 to 50 cm. high, of this ant. But it inhabits at the same time all the hollow branches of the plant. Makanga on the Okiavo River." One may conclude from this that there is no absolute contrast between the carton nest of buchneri and the habit of living in hollow stalks.

Ecology Op Unidentified African Species Of Plectronia In addition to the species just studied, I have found caulinary swellings inhabited by ants on a number of rubiafceous plants which are provisionally regarded as belonging to the genus Plectronia. It is possible, however, that one or more may be species of related genera, such as Vangueria, Grumilea, or Psychotria. At any rate, I have been unable to identify them with any of the described African Rubiaceae and they may even represent forms new to science. Their correct identification will undoubtedly be made later when the study of my herbarium, now in the hands of Mr. De Wildeman, Director ot the Brussels Botanic Garden, is more advanced.

Plectronia species A.—This species was first observed on the forested banks of the Aruwimi River near the village of Bafwalipa, between Bomili and Avakubi (December 29, 1913; Coll. No. 1696). It also occurred in the Ituri Forest, near the village of Tete, between Penge and Irumu (February 22, 1914; Coll. No. 2567), and, in company with Mr. Lang, I came across it again along the Tshopo River near Stanleyville (March 6, 1915; Coll. No. 7043). It is a climbing, much-branched bush of the forest, with simple, opposite, short petiolate or subsessile leaves, which are asymmetric and cordate at the base. There were no thorns or spines on the specimens I examined. The entire plant—leaves and stems —is abundantly covered with long, erect, brownish hairs. The flowers are small and clustered in corymbs in the axils of the leaves.

Myrmecodomatia (Fig. 96) are found on some of the branches only. They consist of spindle-shaped swellings on the lower third of an internode, are about 30 mm. long and 8 mm. thick, and placed immediately above the node. The domatium is a spacious, rather thin-walled cavity. When inhabited, it is almost wholly cleaned of medullary tissue and communicates with the outside by means of a broad, irregular aperture, placed about the middle of the swelling. It was noticeable that leaves at the base of the expanded area are shorter and more heart-shaped than elsewhere on the plant. In this case, too, the enlargements are normal productions and their inner cavity originates through the drying of the pith and without the agency of ants.

[graphic]

Mr. Lang collected specimens of Cataulacus trsegaordhi variety plectronix Wheeler in domatia of this species along the Tshopj River, while I found a few workers of Engramma kohli Forel in other swellings of the same plant.

Plectronia species B.—I obtained this Plectronia in the Rain Forest near Avakubi (January 10, 1914; Coll. No. 1871) and Penge (February « 14, 1914; Coll. No. 2478), in both cases on the banks of the Ituri River. It is a creeper whose main stem, about 20 mm. thick near the ground, hangs freely in true liana-fashion between the bushes, while the branched upper part spreads its leaves over the crowns of low trees and undergrowth. Evidently closely related to the pre- Fig. 96. Phctrmia species

.,. , / . . v . , . n A. Portion of branch in

ceding form (species A), it differs chiefly in being longitudinal section, showing more sparsely hairy, and in having myrmeco- a domatium occupied by ants:

, - , , . e, aperture leading into the

domatia of another shape, furthermore, the main cavity. Drawn from life at stalk bears at the nodes strong thorns placed in BafwaliP". between Bomiii

. p . , i i t t t * andAvakubi, December,1913;

pairs and formed by the hardened bases of natural size, aborted branches.

In this species ants inhabit the thickened main stem, as well as the branches. On the latter the myrmecodomatia (Fig. 97a) are elongate, spindle-shaped swellings of the nodal region, extending about as far below as above the node. They are almost completely excavated and rather thin-walled; their internal cavity is 9 to 11 cm. long, 8 to 10 mm. wide, and even extends a short distance into the slightly swollen bases of the opposite branches. In this case too the expansions are normally present on the plant and their medullary tissue soon dries up, the ants merely piercing the orifices and removing the remains of pith. When occupied by these insects, the domatia usually have a number of apertures, placed above the node in an irregular, longitudinal row; there is often an exit hole also at the enlarged base of the side twigs. Even the nodes of the main stalk (Fig. 96b) are tenanted but, owing to the thickening of

[ocr errors][graphic]

Fig. 97. Plectronia species B; a, portion of younger branch in longitudinal section, showing royrmecodomatium at the node which also extends into the base of the lateral ramification; b, portion of main stalk, showing shape of domatium in older parts of plant; e, apertures leading into the cavity. Drawn from life at Avakubi, January, 1914; natural size.

the woody cylinder, are but slightly or not at all swollen and their inner cavity is much reduced (3 to 4 cm. long, 5 to 7 mm. wide); they usually present two openings placed on a crateriform elevation, one above each of the nodal thorns. Frequently there are scars of other perforations which have been closed by callus growth.

The ants found inside this Plectronia belonged in both localities to a small, unidentified species of Crematogaster which can hardly give protection to its host. Even though most of the domatia were inhabited, the leaves had been eaten by caterpillars and both young branches and leaves bore numerous insect galls—elongate, pear-shaped swellings ending in a recurved tail-like apex and on one side of the tail with a small exit hole leading into a central chamber; their outer surface covered with many erect, brownish-red hairs; all the galls seen were empty.

Plcctroma species C.—In the Semliki Forest, near Lesse (June 15, 1914; Coll. No. 4753), I came across a creeper whose many hanging branches had covered the bushes at the edge of a clearing. It is perhaps specifically identical with the preceding form (species B), possessing most of its general charaters. Yet the domatia are sufficiently different in shape to deserve separate description.

The ant-swellings (Fig. 98) are short and broadly spindle-shaped, and occupy the lower part of the internodes of most of the branches. The inner cavity is very spacious, 6 to 8 cm. long and 15 to 20 mm. wide, continues a little below the node, and extends also into the slightly swollen bases of the side branches. A peculiarity of this Plectronia is that the domatia lack circular apertures, but communicate with the outside by

means of two long slits, placed opposite each other in the upper part of the swelling, above each of the side branches. Often these openings are partly closed by callus growth. The plant at Lesse was inhabited by populous colonies of a small Crematogaster with a queen, numerous workers, and brood at various stages; also coccids which were fixed on the callus tissue near the inner margin of the slits.

[graphic]

Fig. 98. Plectronia species C. Longitudinal section of swollen node inhabited by ants: e, callus growth bordering the slit which leads into the cavity; c, coccids attached to inner walls. Drawn from life at Lesse, June 1914; natural size.

Cuviera de Candolle Cuviera A. De Candolle, 1807, Ann. Mus. Paris, IX, p. 222; 1830, 'Prodromus Eegn. Veget.,' IV, p. 468. Hiern, 1877, in Oliver, 'Flora of Tropical Africa,' III, p. 156. K. Schumann, 1891, in Engler and Prantl, 'Die Natiirl. Pflanzenfam.,' IV, pt. 4, p. 94.

Glabrous shrubs or small trees, rarely with pubeYulent young branches. Leaves usually large, broadly ovate, entire, opposite, coriaceous or leathery; stipules apiculate, united into a short sheeth between the bases of the petioles. Flowers polygamous, with large foliaceous bracteoles, in many-flowered, axillary panicles. Sepals 3 to 5, almost free or shortly united at the base, foliaceous, spreading, often unequal, persistent, much longer than the petals. Corolla hypocrateriform, with a short, straight tube furnished inside with a ring of deflexed hairs, and large, fleshy lobes. Stamens 5, exserted, placed on the mouth of the corollar tube. Ovary 3- or 5-celled, each cell with one ovule. Ovule suspended, with upper micropyle and flattened funiculus. Style with a semiglobose, cap-shaped or mushroom-shaped, sulcate stigma. Fruit an obovate drupe, often oblique or falcate, distinctly ribbed, with 3 to 5 seeds.

[graphic]

Map 46. Distribution of Cumera, a genus of myrmecophytic plants.

Cuviera is a strictly African genus, ot which fourteen species have been described. Its general distribution is shown on Map 46. The genotype, C. acutiflora de Candolle, is found in Upper Guinea. Only one form, C. australis K. Schumann, has been described from South Africa. All the others occur within the limits of Engler's Western Forest Province, either in the Rain, Forest proper or on the forested river banks of the adjoining Savannah, below 3000 feet. With the possible exception of C. australis, all the members of the genus may be myrmecophytes

« ZurückWeiter »