Some of them cause so much irritation that the discharge is very watery (hydragogue cathartics), while others, for example aloes, by acting gently on the lower part of the bowel and on its muscular coat, produce simply a laxative effect.
These hills are densely clothed to their summits with an exuberant growth of olives, figs, myrtles, laurels, oranges, aloes, vines and other sub-tropical plants.
Rocella tinctoria, Lecanora, and formed by fusing extract of aloes with potash.
Tropical flora disappears, and in the semi-desert plains the fleshy, leafless, contorted species of kapsias, mesembryanthemums, aloes and other succulent plants make their appearance.
The vegetation on the western side of the island is much less dense, often appearing as scattered clumps of trees on savannah-like plains rather than continuous forest; while in the south-west, where the rainfall is very scanty, the vegetation is largely of fleshy-leaved and spiny plants - aloes and cacti (the latter introduced), with several species of Euphorbia, as well as numerous lianas, one of which (Intisy) yields india-rubber.