34 R. Marloth, Ph.D., M.A.—Some Adaptions [Feb. 26, 



1. The evaporating surface is considerably reduced, 



either by transferring the function of the leaves to green stems or by 

 developing only leaves of small size or narrow forms. The former case 

 is represented by the genus Stapelia, several species of Euphorbia and 

 the imported Opuntia (prickly pear) ; the latter by the heaths with 

 their needle-shaped leaves; In fact, South Africa is exceedingly rich 

 in plants of this group. The order Bruniaceae and the genus Phylica, 

 which, with the exception of a few members of the latter genus, are 

 peculiar to this country, have such leaves, and there are a great many 

 composites and others which resemble them e.q, ; Metalasia, Stoebe, 

 Helichrysum, Passerina. 



2. The surface of the leaves is impregnated with 

 substances impermeable to water, so that the loss can occur 



only through the stomata. For this purpose either cork, wax or silica 

 is used. By the word cork in this instance is meant the suberine, 

 which changes the ordinary cellulose of the outer wall of the epidermis 

 cells into the special layer called cuticula. This cuticula is often very 

 thick e.g. ; the Aloe, Protea, Welwitschia, and many others with 

 leathery leaves. 



A coating of wax or resin protects a good many species of Rhus, 

 Cotyledon, Protea, and it is principally this peculiarity, in connection 

 with the many hairy plants, which gives to South African vegetation 

 the bluish hue which we so often notice in our scenery. There are 

 several plants which produce wax in considerable quantities. The 

 berries of Myrica cordifolia are covered with so thick a layer, that it 

 is collected and exported. The stems of the candle-bush (Sarcocaulon 

 Burmanni and S. Patersoni) will burn even when green, because the 

 outer bark consists of cork well saturated with wax. On older 

 branches this layer is about one-tenth of an inch thick, but if one extracts 

 the wax by repeatedly boiling it in chloroform, it swells, becoming ten or 

 fifteen times thicker and showing 10 — 30 annual rings, each consisting 

 of numerous layers of cork-cells. On the plant, however, they are 

 glued together by the wax, and form a solid mantle entirely envelop- 

 ing the stem. 



Silica is found principally on rushes and desert grasses. 



3. The communication between the atmosphere and 

 the air within is greatly impeded. This is accomplished in 



various ways. Many plants are covered with hairs, which not only 

 diminish the direct heating effect of the sun's rays, but compel the 

 escaping water-vapour to force its way through a series of narrow 

 channels, thereby necessarily retarding the process. Everlastings 

 {Helichvysum and Helipteruni) and the silver tree {Leucadendron 

 argenteuni) are the most familiar examples. But there are a great 

 many Composites {e.g., Oldenlandia, Euryops, Tarchonanthus), 



