156 



THE PLANT SUCCESSION IN TME TH(JRN VELD. 



are well developed, and whatever view be taken of the origin of 

 thorns,* it cannot be doubted that its foliage is thereby protected 

 against grazing animals. It fruits profusely, and the long in- 

 dehiscent pods hang down below the branches well away from 

 the thorns. The pods ripen irregularly, and some of the seeds 

 may be ripe while the rest of the pod is green and succulent. 

 Insects sometimes enter the pods and destroy the majority of 

 the seeds, but sucli seeds as do ripen are \ery hard and resistant. 

 It is the succulent pod itself, and not the seeds, that is the 

 chief attraction for animals, and herbivorous mammals as well 

 as birds may be the agencies for distribution, though in the 

 case of the ^former probably only very few of the seeds remain 

 undigested. I Goats are particularly fond of the pods, and fatten 

 quickly when fed on them. The passage of the seeds through 

 the animal's body assists in germination, helping to soften the 

 verv hard seed-coat. Otherwise seeds of acacias, it is found. 



"TgiMagnl-' 



Fig'. 1. — DiatiTiiiii illustrating root system of .h'aciti arahica 



var. krattssiana. 



do iKJt germinate readily unless they have been first immersed 

 in boiling water to soften the seed-coat. The seedlings a])pear 

 usually singly through the grass, and not in clumps, but taking 

 into consideration the fact that few of the seeds ripen and 

 many are attacked by insects, while others may lie ungerminated, 

 it is not difftcult to understand why only single seedlings appear. 

 For the first year or two the seedlings suffer from grass-fires, 

 though it is surprising how much they will stand. A young 



*See Bews, J. W., '"The Growth Forms of Natal Plants," Trans. 

 Roy. Soc. S.A. ( 1916.) 



t Since the ahove was written this point has been further investigated. 

 Mr. T. R. Sim kindly collected a large quantity of the ripe pods and for- 

 warded them to Mr. Pole Evans, who arranged with Sir Arnold Theiler 

 for feeding tests to he carried out in the Department of Veterinary 

 Research Numerous samples of seeds were returned to us which had 

 passed through the bodies of herbivores uninjured. My colleaa;ue, Dr. 

 Denison, has made a preliminary chemical analysis of the empty dry pods. 

 Thev are very rich in carbohydrate ^probably sugars V 



