896 J. w. BEWS. 



Apai't from tlie pui'ely physical difficulties of investigating- 

 the coast marshes^, under conditions of usually stifling heat, 

 with swarms of mosquitoes, the plant succession is very easy 

 to follow, since it is clearly marked out by a series of 

 successional zones. It is true that the full succession may 

 be obscured by the frequent omission of certain stages in 

 different localities, owing to abrupt variations in environ- 

 mental conditions, such as the depth or amount of water. 

 The streams often change their courses, and vvlien the sand 

 bars at the river are periodically cut thi'ough the lakes are 

 drained out. The sand-bar slowly re-forms and the water is 

 again dammed back. The drainage alters in consequence of 

 such changes, and there may be correspondingly rapid changes 

 in the vegetation, vlei types giving way to stages which 

 belong to the xerosere, i.e. to grassveld. In addition to 

 this, what may be regarded as the normal succession does 

 not always follow the same course. The purely aquatic stages 

 are followed sometimes by Phragmites and Typha, some- 

 times by a mixture of semi-aquatic species, including many 

 of the smaller Cyperacete, and both these types may 

 be followed by the tall-growing species of Cyperus and 

 Mariscus or both the Phragmites-Typha associes, and 

 the semi-aquatics may be omitted and the Cyperus zone 

 follow on the submerged and floating aquatic stages. It may 

 be well, therefore, to modify the above statement and say 

 that it is easy to follow the succession in any particular vlei, 

 yet it is more difficult to generalise with regard to the coast 

 hydrosere as a whole. 



The stages will be dealt with as far as possible in the order 

 of succession, it being clearly vmderstood that certain stages 

 are more or less of equal rank, as is indicated in the diagram 

 (text-fig, 4). 



(a) Submerged Aquatics. — The chief plants belonging 

 to this earliest stage are the Potamogetons, the species found 

 on the coast-belt being P . n a t a n s , P . 1 u c e n s , P . p u s i 1 1 u s , 

 P. crispus and P. friesii, but they are not, of course, 

 always wholly submerged. Ceratophy Hum demersum 

 (551) is another characteristic species. 



