312 REVISION OF EXTRA- TROPICAL SOUTH AFRICAN ASCLEPIADACE^. 



Flora of Tropical Africa should be confined to those growing north 

 of this line : no attempt should be made to draw a boundary on the 

 east coast as far south as Delagoa Bay, or even farther, as has been 

 done in the three published volumes of the Flora of Tropical Africa. 



Perhaps it may not be out of place to make a few remarks on 

 the geographical distribution of the South African Asclepiadacea:. 



It is certainly interesting and well worth mentioning how very 

 different the distribution of AsclepiadacccB in this country is from 

 that of the Orchids, although they have many points in common, 

 and are adapted to the same mode of fertilization by insects. 

 While the Orchids are fairly equally divided over a belt around 

 the south and east coasts, and are vastly decreasing in number and 

 proportion to the other orders towards the drier interior, the 

 AacicpiadacecB undoubtedly have their head-quarters in the east, and 

 are most distinctly decreasing in number towards the south-west. 



In the south-western region we find only three genera which 

 may be regarded as truly typical to this region — MicroloniaU. Br., 

 EiisU'i/ia R. Br., and Glossostephanus E. Mey. Omitting these three 

 genera, all the Asclepiadaceic in the south-western region seem to be 

 outposts of more or less eastern or northern genera, which have 

 migrated in, for most of them have a decided distribution to the 

 east or north, at any rate they can hardly be regarded as belonging 

 to the same type of flora which by botanists is generally called the 

 true Cape flora, of which the extremely local distributions of many 

 species is a marked feature, and seems to tell for the age of this flora. 



The number of species of Asclepiadacea. in the south-western 

 region is, considering the richness of the whole flora, so small that 

 it would be useless to attempt to ascertain the correct proportion. 

 It may suftice to say that there are to be found hardly fifty different 

 species ; almost half this number being common with either the 

 northern or south-eastern regions. The largest genus here repre- 

 sented is Schizoglossum, with thirteen species, of which only eight 

 are endemic in our region, whereas other five have been recorded 

 from the south-eastern region as well. The Stapeliea mostly occur 

 only where the flora of the Karroo has found its way through the 

 river valleys or deep mountain passes into the south-western regions, 

 or where no sharp boundary exists between these two regions, as 

 is the case in the Clanwilliam district in the north-west. Other 

 genera represented in the south-western region are Astephanus E. Br., 

 Asctepias L., C'ljnanchiim L., Sarcostemma R. Br., Brachystelmaria 

 Schltr., and Secamone R. Br. These comprise seventeen species, of 

 which only six are endemic. 



The " Karroo " and the " Upper Region " are both very similar 

 with regard to their Asclepiadaceous flora. Here the StapeliccB 

 rank by far the highest in number, for here are evidently the head- 

 quarters of the large genus Stapelia and several of the smaller allied 

 genera, such as Huernia, Caralluma, and Duvalia, A rather distinct 

 flora we get towards the Namaqualand coast-belt, out of which may 

 be mentioned several characteristic genera, viz. Ectadlum E. Mey., 

 Piijssolobium E. Mey., Decahelone Dene., Hoodia Dene., and Tricho- 

 caulon N. E. Br. Other genera represented are Microlunia R. Br., 



