;236 PLANT SUCCESSION. 



West of Signal Hill proper is a very deep valley with steep 

 sides; a smaller valley ("valley A"), rising near the head of the 

 "central valley," passes into this. Between the heads of "valley 

 A" and the "central valley" are found the only clumps which 

 occur to the west of the latter. Still further to the west is a line 

 of low hills cut into by deep valleys, but trees are almost entirely 

 absent from the steep sides of these. The slope immediately below 

 our point of vantage, and one further to the east, are the only 

 ones in the neighbourhood on which scattered clumps of trees can 

 be seen. 



Turning now to the east, one notices another valley ("valley 

 B"), and beyond this the hillside just mentioned. Streams of 

 water flow through most, if not all, of these valleys, and in some 

 cases they have cut deeply into the bed of the valley, forming 

 rather deep and narrow dongas. 



The slopes on which the tree veld occurs face almost due north, 

 and consequently receive very strong sunlight throughout the day. 

 The deep narrow valleys to the west receive a much shorter period 

 of illumination each day, and this may explain the absence of tree 

 veld from the adjacent slopes. Exact measurements of insolation 

 have not been made, but the writer has often noticed that at this 

 time of the year the slopes on which the trees occur are in full 

 sunlight until about five o'clock, whereas the western slopes of the 

 deep valleys pass into shade at about half-past three or four 

 o'clock. 



Frosts are probably rare on the hillside, though they are 

 recorded at the Botanic Gardens just below. Even here there is 

 seldom more than 5 degrees of frost, the record of 11 degrees last. 

 year being the lowest known for twenty years. The Gardens are, 

 however, situated at the lowest level in the neighbourhood, and 

 the temperature will be appreciably higher on the slopes investi- 

 gated. The fact that bananas and pineapples are successfully 

 grown at about the same level on a neighbouring hillside indicates 

 the almost complete absence of frost. 



III. Type of Grassland Invaded. 



The dominant grass all over the hillside is Aristida junci- 

 formis, which has almost entirely replaced Themeda (Anthistiria) 

 triandra, probably on account of repeated grass burning. Other 

 grasses present are Andropogon hirtus (subdominant in places), 

 .4. schoenanthns var. versicolor, A. pertusus, A. intermedins var. 

 punctatus, A. eucomis, Eragrostis chalcantha, E. brizoides, 

 Panicum serratum, Sporobohis indicus, Tricholaena rosea. Scat- 

 tered throughout the veld are numerous associated plants, but they 

 were not in flower during the period of investigation, and conse- 

 quently lists of these have not been compiled. Mention must, 

 however, be made of the occurrence in isolated patches of Aloe 

 saponaria and of Vangneria sp., the patches covered by the latter 

 being as a rule the more extensive. Eugenia alhanensis is also 

 fairly common. 



