XX 
THORNS 
259 
plant: it is used, especially in Uganda, for making 
hedges. The tree-like euphorbias 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 quickly destroy their woody neighbours. 
Some of the euphorbias are prickly and the spines 
are arranged in groups 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 candelabra euphorbias will grow in places 
where trees would die from heat and drought. It is, 
however, useful to remember that young trees and 
bushes flourish under the protection of euphorbias, and 
in due time the trees and bushes 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 by 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 
