Function of the Ethereal Oils of Xerophytic Plants. 321 



Less., is highly aromatic in damp weather, and its scent will then 

 accompany you for many miles when travelling in the country. 

 Other plants are Elytropappus glandulosus Less., Belhania 

 genistcefolia L'Her., the so-called pepperbush of the Euggens ; 

 Osteospermum ilicifolium L., of the mountain region, and the 

 gland-covered, sticky 0. spinosum L., of the hills ; Artemisia afra 

 Jacq., the Cape wormwood ; many species of Pelargonium ; 

 Malvastrum capense G. et H., and even a dweller of the woods, 

 Plectranthus fruticosus Lamk. 



All these observations, incomprehensible if the hypothesis on the 

 diathermanic function of the oils be accepted, are, however, in 

 perfect accordance with the view that the oils act as a deterrent 

 to animal enemies, and in particular to those which are to be feared 

 especially in damp weather, viz., snails and slugs. It may be 

 objected that there are no snails or slugs in the veld or on the 

 mountains, as only some of the introduced species have become 

 common in the gardens of the Cape. That is an error. I have 

 found snails as well as slugs on various mountains of the South- 

 West and also in karroid spots, e.g., near Clanwilliam. One must, 

 of course, not expect to see them on a dry summer's day. But 

 when the South-East cloud covers the mountain for days, or when 

 a nice drizzling rain is falling, you are fairly sure to find some, 

 provided that you feel inclined to look for them. In fact, one of 

 the introduced species from the Mediterranean, Limax Gagates, 

 a black slug which is about three inches long, is so common in the 

 upper part of the Platteklip gorge, that on such an occasion one 

 may gather a dozen in a few minutes on the rocks near the top of 

 the mountain. I have also collected an indigenous species of slugs 

 (Oopeltes) and several kinds of snails (Dorcasia, Natalia, and Phasis) 

 on the Winterhoek near Tulbagh and on the Zwartebergen, and I 

 learn from Mr. Lightfoot that there are a fair number of indigenous 

 species of slugs and snails at the Cape, although few of them only 

 are occasionally common. 



In conclusion I may add, that in many cases the protection against 

 grazing animals obtained by means of these oils will be of more 

 importance to the plants than that against snails or caterpillars, but 

 that the little foes would probably rapidly multiply and endanger 

 the existence of many plants if they were not guarded off in such 

 an effective way. 



