466 



NA TURE 



[October 14, 1909 



PERC 



Sf.ADEN MEMORIAL EXPEDITION 

 IN SOUTH-]VEST AFRICA, 1908-9. 



I. 



'HE Percy Sladen Memorial Expedition was tlie out- 

 come of a recent study of Welwitschia, that most 

 ■remarkable of West African plants. Its primary object 







III. ,:,,•: Kii.i -c... I';,,ii„.;. . D.iii, i.. ;.in. North 

 cunctiaied by the lowest zone ot vegetation. 



species characteristic of the dry, low-lying plateaux of 

 Great Nnmaqualand were encountered for the first time. 

 Prominent among these were Tamarix articulata. Aloe 

 dichotoma, Statice scabra, Galenia articulata, Didelta 

 annua, Exomis albicans, and Vogelia africana. This 

 'T'HE Percy Sladen Memorial Expedition was the out- southern extension of the flora of tropical and subtropical 



., — „ „f „ * „i..,i.. „( •n,-„i...:._.i,:.. tu„» — „► Namaqualand seems to be confined to sheltered valleys at 



elevations not exceeding 2000 feet. 



From O'okiep a detour to the north- 

 east across the sandy plains of Bush- 

 manland was rewarded by an un- 

 expectedly rich collection, for unusually 

 heavy rains had recently fallen. The 

 plains were gay with die flowers of 

 Hoodia Gordoni, Rhigozutn sp., and a 

 tall bushy Hermannia. A shrubby 

 .Aristida and some smaller species of 

 the same genus were also very 

 abundantly represented, while trees of 

 Aloe dichotoma and large symmetrical 

 bushes of species of Euphorbia were 

 conspicuous on the " kopjes." The 

 natural vegetation along the banks of 

 the Orange River forms a narrow belt, 

 in which a distinct arrangement in 

 subordinate zones can usually be traced. 

 The lowest zone (Fig. i) consists of a 

 dense scrub of Satix capensis. Acacia 

 Iwrrida, Zizyphus mucronata, and a 

 few other bushes, with some grasses, 

 reeds, and sedges. Above the primary 

 bank of the river the mountains rise 

 steep, rugged and barren, or, between 

 them and the stream, are stony flats 

 (Fig. i) all but devoid of vegetation. 

 Having returned to O'okiep to refit, 

 we arrived at Raman's Drift for the 

 second time on January 22, and crossed 



was the investigation of the biology and morphology of | to the German side on January 24. The river at this 



Gnetum africanum, the only immediate relative of Welwit- j time was in flood, and its muddy waters were some 



schia known to occur south of the Congo. It was further 



proposed to examine, so far as circumstances would allow, ~ I 



ihe flora of the desert-belt and of the regions adjacent to 



.it. The expedition was under the auspices of the trustees \ 



•of the Percy Sladen Memorial Fund, and was assisted by 



■a grant of 200/. from the Royal Society. During the first 



section of the journey (Cape Town to Liideritzbucht) I 



was fortunately able to travel in company with the mag- 

 netic survey expedition of the Carnegie Institute under my 



colleague, Dr. J. C. Beattie. A saving of half the 



■ordinary cost of transport was thus effected. The route 



followed was very largely determined by the distribution of 



the usually widely separated water-holes. What would 



■certainly have proved a very interesting part of the journey 



(viz. from Keetmanshoep to Windhuk) had to be abandoned 



owing to the necessity of arriving in central Angola before 



the end of the season in which suitable stages of the 



ovules of Gnetum were likely to be obtainable. 



Leaving Ceres Road Station on November 26 with a 



waggon drawn by twenty oxen, we ascended to the Ceres 



Plateau (iioo feet) through Mitchell's Pass in the Lange- 



berge Range, and travelled for four days over an un- 

 dulating tableland rising to 2500 feet, the flora of which 



Is closely related to that of the mountainous districts of 



south-western Cape Colony. Unfortunately, most of thi- 



country was suffering from drought, and the botanic.il 



results were poor. At Karoo Poort we suddenly emergiil 



upon the western tongue of the Karoo (November 311), 



which was crossed in six days. Here also the ground 



was parched ; in some districts, it was stated, no rain 



had fallen for four years, and many of the farmers had 



migrated with their families and flocks into Bushmanland 



and other more favoured localities leaving their honn - 



steads unoccupied. Over large areas all the non-succulent 



vegetation had disappeared and the flora consisted almost 



entirely of Augea capensis with a few species of Mesem- 



brianthemum. Ascending the Blauwkrantz Pass in a spur 



of the Roggeveld Range on December 6, we came upon a 



plateau the flora of which is closelv related to that of the 



Niouveldt Mountains in the neighbourhood of Beaufort 



West. On December 10 a somewhat sudden descent to I 



1600 feet brought us again into a karoid region, in which | 

 NO. 20S5, VOL. 81] 



■W 



If 





'ij»»^i*' * 'M 



Fn.. -■,— Great Namaqualand south of .^. ;, i . i 



Kiiphorbia s/>. The native is a P>ondt:!zwaarl. 



600 yards wide at the drift. A few hours of heavy 

 travelling brought us upon a plateau (2300-4000 feet) 



