supply the needs of 130,000,000 people on the basis of the imperfect statistics and inadequate data of the past, becomes almost an impertinence. It is much more probable that the 400,000 square miles which now meet the needs of 75,000,000 people, with an enormous excess for export, will in 1930 still suffice for the domestic supply of 130,000,000 people, with a proportionate export corresponding to the present.
If the product of the farms of the West now yielding the largest crops, or of the renovated lands of the South now yielding the best crops, be taken as the average standard of the near future, as they should be, then it may be true in 1930, as it is now, that one fifth of the arable land of this country when put under the plow will still suffice for all existing demands, the remainder of our great domain extending the promise of future abundance and welfare to the yet greater numbers who will occupy the land a century hence.
I may add that in the course of a very friendly correspondence with Sir William Crookes, while we are still at variance in our estimates of the area which may be converted to the production of wheat in this country without trenching upon any other product, we are wholly at an agreement on a most material point. I quote from one of his letters: "Under the present wasteful method of cultivation there will be in a limited number of years an insufficient supply of wheat. Apply artificial fertilizers judiciously, and the supply may be increased indefinitely." I would only venture to add to the judgment of so eminent a writer the words "or natural," to the end that the paragraph should read, "Apply artificial or natural fertilizers judiciously, and the supply can be increased. indefinitely."
Many years ago I was asked among others, "What would be the next great discovery of science or invention?" To which I replied, "A supply of nitrogen at low cost." Has not that discovery been made in the recent development of the functions of the bacteria which, living and dying upon the leguminous plants, dissociate the nitrogen of the atmosphere and convert it through the plant to the renovation of the soil? Is not the invention of methods of nitrifying the soil by distributing the germs of bacteria one of the most wonderful discoveries of science ever yet attained? Can any one yet measure the potential of any given area of land in any part of this country in the production of any one of its great crops? That there is a limit may be admitted. Can any one venture to say that any of our average crops yet approach beyond a small fractional measure the true limit of production, whatever it may be, either in cotton, maize, wheat, or any other product of the soil?
In this, as in many other developments of the theory of evolution, the factor of mental energy, which is the prime factor in all material