THE EFFECTS OF DROUGHTS AND OF SOME OTHER 



CAUSES ON THE DISTRIBUTION OF PLANTS 



IN THE CAPE REGION. 



By I'rof. Rudolf Marluth, M.A., Ph.D. 



One of the special features of the flora of the south-western 

 corner of South Africa, the Cape region, which extends from the 

 Bokkeveldberg to the Van Staden Mountains near Algoa Bay, 

 is the limited area occupied by many of its species. Quite a 

 number of plants are known only from one particular locality, 

 or a small district. Some of the best-known examples of this 

 mode of occurrence are Leitcadciidroii argenteuin, the silver 

 tree; Autholysa Mcrianclla, called " flames " ; Disa piirpurascens, 

 a near ally of Disa graminifolia, the well-known "blue disa"; 

 Cyti'nus capcnsis, hitherto found only near Zeekoe \lei* ; Scr- 

 riiria florlda, which is known only from a valley on the upper 

 Berg River, etc. 



Various causes have contributed to produce this state, the 

 principal one being the great age of the Cape flora, which dates 

 back into early tertiary times, or ])robably even further. But 

 some of the peculiarities of distribution must be due to other 

 causes, and some of these are operating even at the present dav. 

 The difficulty, however, is the shortness of the life of an 

 observer in comparison to the fluctuations in the plant covering 

 of a district, where no interference of man takes place, and the 

 absence of records of sufficient accuracy in order to prove such 

 changes. 



Every instance in which such a change can l)e definitely 

 established is consecjuently of unusual interest from a phvto- 

 geographical p<;)int of view, and the few observations which I 

 am able to submit here are the first of their kind recorded in 

 South Africa. These observations are of three kinds: 



I. The s])ontaneous disappearance of a species from a 

 locality without an}- apparent reason. 

 II. The disappearance of a s])ecies from a locality due to a 

 natural change of the conditions of its existence. 

 IIL The impoverishment of the flora of a locality, and ])er- 

 haps of a district, through climatic conditions, viz., an 

 unusually severe drought. 



I. The Disappear.ance of a Species from a Locality witiiott 

 THE Interference of Man or Climate. 



A striking illustration of the gradual spreading and sudden 

 disappearing of a species without the interference of man bv 

 means of veld fires, draining, etc., was afforded recently on the 

 southern slopes of Table Mountain at an altitude of about 2,700 

 feet. The locality is above tlie nuarrv at the Hely-Hutchinson 



The author has since received a specimen from Saldanha Bay also. 



