Plate 102.
MESEMBRYANTHEMUM digitatum.
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.