TRANSACTIONS OF SECTION K. 685 
is in line with the axis of rotation: under these conditions the hypocotyl curves 
away from the centre in obedience to the stimulus arising in the cotyledon. If 
geo-perception were confined to the hypocotyl the curvature must have been 
towards the centre. 
4. A Botanical Excursion in the Welwitschia Desert. 
By Professor H. H. W. Pearson, Sc.D., F.L.S. 
Welwitschia is confined to the littoral strip of desert which, commencing near 
the mouth of the Orange River, extends northwards far into the tropics. The 
paper records observations ! made in 1907 in the neighbourhood of Haikamchab 
and Welwitsch, situated in the most southern area from which the plant is known. 
The flora of the desert belt (the ‘ Namib’) is of a marked desert type, mainly 
characterised by several highly peculiar and endemic forms. The western fringe 
of the Namib is occupied by sand-dunes, some of which are as much as 200 feet 
high. Their vegetation is very scanty, and it appears that the whole pbanero- 
gamic flora of the dunes of Walfisch Bay comprises no more than a dozen species. 
Of these, two are of special interest, viz., Acanthosicyos horrida and Tamarix 
articulata, The former, a member of the Cucurbitacez, is well adapted to growth 
in accumulations of sand, and many of the large dunes owe their stability, and 
indeed their existence, to this plant, whose deep roots serve as anchors, 
East of the sand-dunes, where the surface is hard, the flora is richer in species, 
though in many localities considerable areas are quite destitute of flowering plants. 
The vegetation consists chiefly of deep-rooted woody perennials of low habit and 
with small leaves. Among these are Zygophyllum Stapfii, a very characteristic 
Namib plant, and one of the surprisingly few succulents met with, Commiphora 
saxicola, Sarcocaulon sp., whose stems are encased in an armour of hard wax, a 
Bauhinia, a few Capparidacez and Blepharids. The grasses are rather numerously 
represented in sandy places by species of Aristida, and prostrate Cucurbitaces are 
not infrequent. The arborescent Aloe dichotoma is common among the barren 
crags of the broken country overlooking the main river-beds. 
Welwitschia occurs abundantly on the Namib plateau, and descends the ravines 
leading down to the deeper river-channels. Its altitudinal range is about 400 feet. 
A number of photographs illustrating the habit of the plant, its inflorescences, 
cones and flowers, were shown. Pollination is mainly, if not entirely, effected 
by the hemipteron Odontopus sexpunctulatus, as has already been described.” 
Subfoliar inflorescences commonly occur. 
Fertilisation rarely fails, and very large numbers of fertile seeds are pro- 
duced. No germinating seeds nor young seedlings were found, and it appears that 
the conditions necessary for effective reproduction rarely occur, 
The Namib flora must be regarded as of great age, and it must be supposed 
that the climatic conditions at present prevailing in South-west Africa, especially 
the distribution of the rainfall, have, in their mean features, been permanent for 
an enormously long period. Although now so distinct the flora is probably derived 
from the same stock as the Acacia formation which flourishes to the east of it, 
and which in a former period may perhaps have extended considerably to the west 
of its present limit. 
5, Report on the Registration of Botanical Photographs. 
See Reports, p. 417. 
6. Report on Research on South African Cycads and on Welwitschia. 
See Reports, p. 408. 
? Assisted by a grant from the British Association. 
* Nature, vol, Ixxv. pp. 536, 537. 
