74 



The Canadian Field-Naturalist. 



Vol. XXXV. 



A BOTANICAL TRIP THROUGH GERMAN SOUTH-WEST AFRICA. 



By W. p. Thompson. 



In 1912 the writer visited the former 

 German colony in south-west Africa chief- 

 ly in order to secure material of Tiimhoa 

 (Welwitschia) inirahilis, mirabilis both 

 from the morphological and physiological 

 standpoints. It was necessary to make a 

 trip across a very extreme desert whose 

 scanty flora exhibits remarkable xero- 

 phytic adaptations. The conquering of 

 this colony by the late General Botha and 

 General Smuts and the future probable re- 

 lationship of the territory to the British 

 Empire under a mandatory^ held by the 

 Union of Soutji Africa may lend a special 

 interest to the following notes on that 

 trip. 



Landing at Swakopmund on the west 

 coast, one is in a region in wdiich, accord- 

 ing to the official German records, the 

 rainfall averages about one inch a year, 

 though many years may pass with no pre- 

 cipitation. At the time of my visit the 

 natives could not remember when tjie last 

 rain had fallen but were sure that when- 

 ever it was it had been onlj^ a sprinkle. 

 As one proceeds eastward the rainfall in- 

 creases slightly but at no place amounts 

 to more than ten inches annually. Ap- 

 parently in all this portion of the conti- 

 nent the rainbearing winds cross Africa 

 from the Indian Ocean losing their mois- 

 ture on the way. The natives stated that 

 t^e sprinkles always came from the east. 

 In the British territories across to the east 

 coast the rainfall is much heavier. 



This distribution of moisture available 

 for the vegetation is modified in a remark- 

 able way by the fact that several old dry 

 river beds cross the colony from east to 

 west. Apparently the climate was for- 

 merly much moister than at present. Oc- 

 casionally heavy rains in the British ter- 

 ritories to t;ie ea.st cause the water to flow 

 down these old river beds. Sometimes the 

 flood nearly reaches the sea before being 

 ai>sorbed. Foi- long afterwards these val- 

 leys support i\ vegetation different from 

 that of the suirouiiding desert. They are 

 then long band-like oases. 



For many miles from Swakopmund, out- 

 side the dry bed of the Swakop, one can 

 find only three species of plants and very 



few specimens of them (a Zigophyllum, 

 a Mesemhryanthemnm and an Arthaerua) . 

 They look like jtiaycocks on an immense 

 field of sand. In addition to the lack of 

 moisture these plants have to contend with 

 the continually wind-driven sand. All day 

 long the presence of the fine particles of 

 sand in the air makes the horizon as highly 

 colored as one of our sunsets. The sand 

 lodges against the plants and tends to sub- 

 merge them while t,he plants strive to sur- 

 mount the rising sand. In this w^ay high 

 dunes are built up round a single plant. 

 Usually the plant is beaten in the strug- 

 gle with the sand which later blows away 

 and leaves the dead plant exposed. The 

 only other vegetation of this strip near the 

 sea consists of numerous orange-colored 

 lic.hens on the desert rocks. These appear 

 to derive their moisture from the heavy 

 dews, so heavy that on many mornings 

 they drip off the roofs of the houses in 

 Swakopmund. In fact it is difficult to 

 see how even the flow^ering plants can sur- 

 vive unless they utilize these dews. 



As we went inland by broad-wdieeled 

 carts following the route from Swakop- 

 mund to AVindhuk (the capital) later fol- 

 lowed by General Bot/ia, w'e found new 

 plants making their appearance as increas- 

 ing moisture enabled them to survive. Af- 

 ter a time we met outlying specimens of 

 the famous ''good Karoo bush" {Augea) 

 on which the still more famous sheep of 

 the South African farmer largely subsist. 

 At fifty miles from the coa.st we found 

 Tumhou, the chief object of the trip. 



This remarkable plant is like a huge 

 turnip bearing througjtiout its life only 

 two leaves which soon become torn to nar- 

 row shreds by the wind. In adult speci- 

 mens the body is five or six feet in diam- 

 eter and the leaves stretch for twenty feet 

 across the desert sand. As the plants may 

 be more than one hundred years old the 

 length of life of its two leaves far exceeds 

 that of any other knowii leaves. The 

 centre of tjie turnip rots away leaving a 

 narrow atoll-like rim of stem above the 

 sand. Tumhoa is a member of the order 

 Gnetales, the highest of the Gymnosperms 

 which .show in nearly every sti-ncture ap- 



