Plate 102. MESEMBRYANTHEMUM digitatum.
Reading edition
Cape Province.
Ficoideae. Tribe Mesembryeae. Mesembryanthemum, Linn.; Benth. et Hook. f. Gen. Plant. vol. i. p. 853.
Mesembryanthemum digitatum, Ait. Hort. Kew. ed. 1, vol. ii. p. 181 (1789); M. digitiforme, Thunb. in Acad. Leop.-Car. Ephem., vol. viii. Append, p. 6 (1791); Thunb. Fl. Cap. p. 412; Fl. Cap. vol. ii. p. 405.
This curious Mesembryanthemum was first collected by Carl Thunberg between the Oliphants River and the Bokkeveld Mountains about 150 years ago. Thunberg described his plant in 1789, and in his herbarium there is one sheet with two perfect growths and two flowers upon it. Marloth (Flora of South Africa, Pl. 49) figures a small portion of a plant which, he states, was collected at Van Rhynsdorp by Mr. W. Spilhaus and was as large as a child’s head. The specimens from which our illustration was made were collected in the same locality by Mr. E. Rood and sent to the Division of Botany, Pretoria.
The corpuscula, which are very succulent, show an extremely interesting structure when examined in detail. If a longitudinal section is made, a hard green central core is seen, which is the stem; this is surrounded by long, crystalline cells, and the whole covered in by a juicy tissue. As the green tissue is buried in the stem, it is very probable that the crystalline cells referred to act as lenses and concentrate any light which penetrates the outer tissue on to the chlorophyll-bearing cells. The fleshy leaves are almost devoid of chlorophyll.
The flower is borne at the apex of the stem, but this can only be satisfactorily seen in a longitudinal section. The crystalline cells are continued round the base of the calyx.
Description:—Acaulescent plant with woody underground stems and fleshy aerial stems and leaves. Stems 2-3 cm. long, 2-2·5 cm. in diameter, very succulent, glabrous. Leaves two to each stem, usually one larger than the other, 1·5-2 cm. long, 0·8-1·3 cm. in diameter, terete, blunt, very succulent, glabrous. Flowers white, arising from the apex of the stems but appearing on a casual examination to come from the base of one of the leaves, when expanded 1·2-1·5 cm. in diameter. Petals in more than one row; the outermost row connate into definite groups, 7 mm. long, less than 0·5 mm. broad, linear, subacute. Stamens in four rows; filaments 1 mm. long, filiform; anthers about 1 mm. long, oblong. Calyx covered with crystalline cells; lobes almost membranous, 1 cm. long, 3 mm. broad, oblong, or oblong ovate, obtuse. Ovary sunk in tissue of stem, 5-celled, with several stalked ovules with axile placentation; upper portion of ovary cone-shaped tipped with five terete, acute styles each 1 mm. long.
Plate 102.—Fig. 1, longitudinal section of stem showing sheath of crystalline cells and flower embedded at apex; 2, longitudinal section of flower; 3, sepal; 4, top of ovary showing the five stigmas; 5, cross section of ovary.
F.P.S.A., 1923.
