“ The Karroo ” in August . 
109 
of the root-systems of the latter species descends vertically into the 
soil in the ordinary way, while the other, which consists of roots 
given off laterally near the base of the main root, spreads 
horizontally just under the surface of the soil. It would seem 
probable that this horizontal root-system is more especially con¬ 
cerned with the absorption of moisture available after slight 
Fig. 20. Mesembrianthemum sp. (About one half natural size), 
showers, or heavy dews, and which would scarcely soak in to a 
sufficient depth in the soil to be absorbed by a vertical root-system. 
Such is the explanation given by Volkens 1 of the superficial lateral 
roots of species of Diplotaxis and Euphorbia found in the Egyptian 
deserts. We also noticed a similar horizontal spreading of the 
roots in a species of Bulbine (Text-fig. 23). 
The Crassulaceze exhibit some remarkable succulent forms. 
Especially prominent are three shrubby species of Cotyledon. Of 
these, C. fascicularis~ is the largest. It attains a height of some 
three to four feet, and has enormously thick stems. The stem of 
one large specimen which we measured, had a girth of 3 feet 11 
inches. On account of the extreme softness of these large water¬ 
storing stems, the plant is locally known as the “Butter-tree.” 
C. Eckloniana is another striking species (Fig. 2, PI. VII.) In 
both these species, and also in the smaller C. reticulata, the 
axes of the inflorescence, and frequently the dry, opened fruits, persist 
after flowering (see figures cited above). In the latter species they 
become considerably hardened, and form a fairly dense network, 
which spreads as a canopy over the foliage beneath. Possibly this 
1 G. Volkens, Die Flora der A3gyptisch-Arabischen Wiiste, Berlin, 
1887, p. 24. 
Several plants of this species are to be seen in the foreground of 
Fig. 1, PI. VI. 
1 
