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Their leaves are generally adapted to resist any injury from the strong glare of the sunshine. The gums, already alluded to, are also very important, for any crack or break in the tree is promptly gummed up, and there is no loss of precious water thereby. This gum will also prevent or discourage burrowing and boring insects from getting in; they would, if they tried to do so, become "flies in amber," like those found in fossil resin. The trees are generally provided with strong spines, which guard them from the many grazing animals which try to devour the succulent leaflets.