There was but one solution. The human body would have to inure itself to the poison, or it was doomed to extinction. It finally developed a toleration for the gas that had wiped out race after race and nation after nation, but at a terrible cost. Lungs increased in size to secure the oxygen on which life depended, but the poison, inhaled at every breath, left the few survivors sickly and filled with a perpetual weariness. Their minds lacked the energy to cope with new problems or transmit the knowledge which in one degree or another, they possessed. And after thirty thousand years, Burl, a direct descendant of the first president of the Universal Republic, crept through a forest of toadstools and fungus growths. He was ignorant of fire, or metals, of the uses of stone and wood. A single garment covered him. His language was a scanty group of a few hundred labial sounds, conveying no abstractions and few concrete things. He was ignorant of the uses of wood. There was no wood in the scanty territory furtively inhabited by his tribe. With the increase in heat and humidity the trees had begun to die out. Those of northern climes went first, the oaks, the cedars, the maples. Then the pines--the beeches went early--the cypresses, and finally even the forests of the jungles vanished. Only grasses and reeds, bamboos and their kin, were able to flourish in the new, steaming atmosphere. The thick jungles gave place to dense thickets of grasses and ferns, now become treeferns again. And then the fungi took their place. Flourishing as never before, flourishing on a planet of torrid heat and perpetual miasma, on whose surface the sun never shone directly because of an ever-thickening bank of clouds that hung sullenly overhead, the fungi sprang up. About the dank pools that festered over the surface of the earth, fungus growths began to cluster. Of every imaginable shade and color, of all monstrous forms and malignant purposes, of huge size and flabby volume, they spread over the land. The grasses and ferns gave place to them. Squat footstools, flaking molds, evil-smelling yeasts, vast mounds of fungi inextricably mingled as to species, but growing, forever growing and exhaling an odor of dark places. The strange growths now grouped themselves in forests, horrible travesties on the vegetation they had succeeded. They grew and grew with feverish intensity beneath a clouded or a haze-obscured sky, while above them fluttered gigantic butterflies and huge moths, sipping daintily of their corruption.