290 
Bews. — Plant Succession and 
extreme south-west. The list for Natal is that by Medley Wood ( 22 ), and 
that for the Cape Peninsula by Bolus and Wolley-Dod ( 10 ). The former 
contains a total of nearly 3,500 species, and the latter over 2,000. There 
are 320 species common to both °(not including ferns). Ourobject is to see 
whether ecologically these widely distributed species have anything in 
common, and, if so, whether such features differ from those possessed 
by species with a more restricted range. 
Of the 320 species, 60, or 19 per cent., are ruderals, many of them 
introduced, and that probably at different points. At any rate, it has always 
been recognized that common weeds spread very rapidly. This is due 
partly to man’s interference with natural conditions, partly to the fact that 
ruderal species are all good colonizers, and are spread rapidly either by the 
abundance of their seed production or by efficient vegetative reproduction. 
The class as a whole is distinguished by belonging to early stages ol 
successions, the initial stages chiefly of various subseres, if we use Clements’s 
system of nomenclature ( 11 ). Ruderals are killed out by taller growing 
species in the later stages of the succession. Annual plants (Therophytes) 
are common among these ruderals, and the majority of such annuals are 
widespread in South Africa, though other classes of annual plants are not. 
Another 65 out of the 320 species are aquatic or marsh plants. There 
are 26 species of Cyperaceae, common to the Cape Peninsula and Natal, 
7 Juncaceae, including the Palmiet ( Prionum palmita ) which forms large 
consocies, 5 Naiadaceae, and many other isolated species, e. g. Nymphaea 
stellata , Gunner a per pensa> Epilobium hirsutum, Limosellaaquatica, Utricu - 
laria livida , Typha capensis , Phragniites communis , Agrostis lachnantha , 
DiplacJme fusca , Polypogon monspeliensis . 
It has long been realized by ecologists that water and marsh 
plants tend to have a wide distribution, and that the floristic composi- 
tion of marsh vegetation tends to vary but little, even in different clima- 
tic areas, or with increase of altitude, &c. This ‘fact was pointed out in 
detailed ecological papers dealing with the vegetation of Natal ( 2 , 4 ). 
Water presents a relatively uniform environment everywhere, but it is 
also a relatively unstable one. Water and marsh plants belong to the 
initial stages of the hydrosere, so that this large class of widely distri- 
buted plants, like the ruderals, have this feature in common, they belong 
to early stages of the succession. These two classes absorb between 
them 125 species, or 39 per cent, of the 320. 
The remaining 195 species belong to the xerosere. Among them are 
included many Drakensberg species, e. g. Metalasia muricata , Stoebe 
cinerea , Erica cerinthoides , E. hispidida , species of Helickrysum, &c., which, 
as already mentioned, represent outliers of the south-western flora on the 
eastern mountains (though a great many such Drakensberg species which 
are really south-western do not extend quite so far west as the Cape 
