Burl leaned heavily upon his club and watched dully. He could run no more. The army ants were spreading everywhere over the mass of fungus. They would reach him soon. Far to the right the vapor thickened. A column of smoke arose. What Burl did not know and would never know was that far down in the interior of that compressed mass of fungus, slow oxidization had been going on. The temperature of the interior had been raised. In the darkness and the dampness deep down in the hills, spontaneous combustion had begun. Just as the vast piles of coal the railroad companies of thirty thousand years before had gathered together sometimes began to burn fiercely in their interiors, and just as the farmers' piles of damp straw suddenly burst into fierce flames from no cause, so these huge piles of tinder-like mushrooms had been burning slowly within themselves. There had been no flames, because the surface remained intact and nearly air-tight. But when the army ants began to tear at the edible surfaces despite the heat they encountered, fresh air found its way to the smouldering masses of fungus. The slow combustion became rapid combustion. The dull heat became fierce flames. The slow trickle of thin smoke became a huge column of thick, choking, acrid stuff that set the army ants that breathed it into spasms of convulsive writhing. From a dozen points the flames burst out. A dozen or more columns of blinding smoke rose to the heavens. A pall of fume-laden smoke gathered above the range of purple hills, while Burl watched apathetically. And the serried ranks of army ants marched on to the widening furnaces that awaited them. They had recoiled from the river, because their instinct had warned them. Thirty thousand years without danger from fire, however, had let their racial fear of fire die out. They marched into the blazing orifices they had opened in the hills, snapping with their mandibles at the leaping flames, springing at the glowing tinder. * * * * * The blazing area widened, as the purple surface was undermined and fell in. Burl watched the phenomenon without comprehension and even without thankfulness. He stood, panting more and more slowly, breathing more and more easily, until the glow from the approaching flames reddened his skin and the acrid smoke made tears flow from his eyes. Then he retreated slowly, leaning on his club and looking back. The black wave of the army ants was sweeping into the fire, sweeping into the incredible heat of that carbonized material burning with an open flame. At last there were only the little bodies of stragglers from the great ant-army, scurrying here and there over the ground their comrades had denuded of all living things. The bodies of the main army had vanished--burnt to crisp ashes in the furnace of the hills.