172 THE I'LANT SUCCESSION TN IllK THORN VELD, 



Plate 6, b. — Donga showing the root system of Acacia arabica. var. 

 kraiissiaiia. The main taproot descends to the deeper water supplies. 

 Large lateral roots spread out along the surface. 



Plate 7, a. — Base of colonization in a ravine. For full list of species 

 occurring here, sec p. 3. 



Plate 7 /'• — Invasion of the grass veld by thorn trees. Note the 

 presence of termites' nests and young thorn trees in the foreground. 

 The base of colonization extends across the middle background. 



Plate 8, a. — Subsequent species growing up underneath tlie pioneer 

 acacia. Randia rudis. Ehretia hotteiifofica. Celastms buxifolins, Hippo- 

 bromus alata. Hnclea lanceolata. Jasiuumni iiiultipartifiiiii. J. gcrravdi 

 and a climbing asparagus over the top. 



Plate 8, b. — Further stage in succession. The pioneer acacia being 

 killed by the subsequent species. Elceodendron ccthiopicuni, Hippobromus 

 alata. Celastrus buxifolius, Asparagus sp., Rhus sp., Asimn tetracantha. 

 Randia rudis, Euclea lanceolata. Jasminum gerrardi, with Sauseviera 

 thyrsiflora and Hncrnia hystrix abundant as undergrowth. 



Plate 9, ((. — Thorn thicket. Acacia arabica, var. kraussiana. domin- 

 ant. Acacia horrida also present. The foreground shows the succession 

 from grass veld. 



Plate 9, b. — Grass veld with nests of Tcrnies trincr^'ius. Early 

 spring condition. This was formerly Tliorn \'eld. but the trees have 

 l)een cut down for firewood. 



(Read. July 4. 1917. ) 



EINSTEIN'S Theory of Gravitation. — Sir F. W. 



Dy.son* observes that, according to Einstein's theory, a ray of 

 light grazing the sun's limb should be deflected. Photographs 

 taken ])y Davidson with the astrographic e(|uatorial, on the 

 occasion of the .solar eclipse of 1905, have been examined, but 

 the results were not sufficiently accordant, and it is suggested 

 that special arrangements should be made to ol)tain photographs 

 during the eclipse of May 29th, 1919, for the critical analysis 

 of the effect. A list of stars available for instruments of the 

 astrographic type has been prepared, together with the computed 

 displacement that shottld be shown if the theor}' be correct. 



* Roy. Astroii. Soe., .1/..^'. 77, 445-4.17, March. 1917. 



