XX THORNS 259 



plant : it is used, especially in Uganda, for making 

 hedges. The treedike cii[)horbias fill in Africa the 

 place supplied by the cactus in Central America., and 

 they are used in the same way for fencing estates and 

 gardens ; slips from them easily take root. Euphorbias 

 are often seen forming isolated clumps in districts 

 where trees are scarce or absent, because their milky 

 trunks and branches preserve them against grass fires 

 which C[uickly destroy their woody neighbours. 



Some of the euphorbias are prickly and the spines 

 are arranged in gr(jups of three. The middle spine, 

 usually larger than its lateral companions, is often 

 absent. Morphologically the three spines represent a 

 leaf and two stipules. For example, at the base of the 

 leaf-stalk of a willow (salix), there are two stipules ; 

 in the case of the euphorbia the large central spine is a 

 modified leaf and the smaller lateral spines represent 

 the stipules. The thorns are easily detached. I have 

 examined many branches on many euphorbias, young 

 and old, without finding the middle spine : the lateral 

 prickles are very constant. 



The candelal:)ra euphorbias will grow in places 

 where trees would die from heat and drouoht. It is, 

 however, useful to rememl)er that young trees and 

 bushes floui'ish under the protection of euphorbias, and 

 in due time the trees and l.)ushes grow and stifle their 

 protectors. It is also a fact that a forest cannot arise 

 without the aid of bushes, as they protect the young 

 trees from being nibbled and destroyed l)y grazing and 

 browsing mammals. 



The consideration of the candelabra euphorbia leads 

 to another matter of deep interest. Many parts of East 

 Africa are covered with forests ; the tangle of bushes, 

 creepers, and trailing plants is so dense that such forests 

 are impenetrable unless the traveller follows the tracks 

 made by large game, or has a pathway cut by axes. 



After leaving the thick forests of the Mau escarpment 

 the scenery downwards to the Victoria Nyanza under- 



s 2 



