THERE have always been those who delight in prophesying catastrophes to the human race, just as there have always been those who do not listen to them. The future of mankind may, indeed, be violently affected by some unexpected and extremely disconcerting cosmic disturbance; it is certain to be influenced in a less spectacular although equally impressive manner by limitations in the natural productivity of the earth's surface, and in the extent of the remaining reserve areas of virgin soil. In a mere comparison of rates of productivity we appear to have ample material wherewith those so minded can, without much risk of contradiction, anticipate a first-class human disaster; we also have an indication that the so-called ‘nitrogen problem’ is not a transient condition, but a situation which in our own day needs courageous, systematic, and world-wide measures for its solution. We may assume that between a date which remains controversial and A.D. 1800 (perhaps half a million years, perhaps more) the population of this earth reached 800 millions of human beings, whilst from A.D. 1800 to 1900 it rose to 1730 millions; if this rate of increase continues—and there is no reason to anticipate the contrary—an early intersection of the population curve and the soil productivity curve is necessarily to be expected. Indeed, it has been estimated that the present methods of farming will lead to a definite food scarcity before the end of the present century.