36 R. Mar loth, Ph.D., M.A. — Some Adaptions [Feb. 26, 



This peculiarity is almost as strongly exhibited by our indigenous 

 Protect grandiflora (waageboom). In this species only the very base 

 of the sessile leaf is horizontal ; immediately above the base the leaf is 

 so twisted as to become vertical and a mere edge is presented to the 

 rays of the burning sun. 



Some other plants, mostly belonging to the order Leguminosae, 

 perform periodical movements with their leaves or leaflets. Most 

 species of Oxalis, several Acacias e.g. A. Giraffae, detinens, tenax, 

 horrida and Cassia obovata fold up their leaflets during the hottest 

 part of the day and open them again in the afternoon. 



5. Plants Which pOSSeSS reservoirs, either underground or 

 in their stems and leaves. The Elephantorhiza Burchellii is a delicate 

 herb, one or two feet high, but it possesses a huge watery rhizome, 

 sometimes weighing ten pounds. Several asclepiads of the Kalahari 

 region accumulate so much water in their large tubers that the Bushmen 

 often depend entirely on it. 



The Stapelias and Euphoi^bias store the water in their stems like 

 the imported Cacteae and retain it with great tenacity. This is the 

 reason why it is so difficult to kill such a plant, for every separate 

 bit carries enough water and food material for the production 

 of new roots and buds. A remarkable plant of this kind is the 

 Cissus Cramerianus of Damaraland, a near ally of the vine. It has 

 a fleshy trunk often ten feet high, with a diameter of two feet at its 

 base, and forms only a few thick branches. A similar trunk of smaller 

 dimensions has Cotyledon fascicularis of the Hex River district. 



Most succulents utilise the leaves as a store room. A section 

 through an Aloe leaf shows that the green cells form only a thin layer 

 round a colourless watery tissue. We can make the same observation 

 about many others. Almost all species of Cotyledon, Crassula and 

 Mesembryanthemum, e.g., M. acinaciforme (Hottentot's fig) possess a 

 similar structure, not to mention Augea capensis, several Zygophylla 

 and Poi*tulacaria afra, the celebrated spekboom. But the water 

 tissue is not always in the centre of the leaves. Many species of 

 Mesembryanthemiim e.g. M. crystallinum develop their epidermis 

 cells into little vesicles, which give the leaves such a shiny appear- 

 ance. Many orchids e.g. Satyrium carneum, Holothrix possess 

 epidermis cells of such a height that this layer of water forms the 

 greater part of the mass of the leaf. With Haemanthus it is the 

 same. The little Peperomia retusa, an inhabitant of moist and shady 

 places, provides still better for the times of drought, for its epidermis 

 is multiplied, being several times thicker than the green tissue, cover- 

 ing it like a sponge. 



6. The sap contains certain substances which 



prevent rapid evaporation* Such substances are slime, gum 



