"Agriculture, as well as other industries, has received large benefits from the systematic investigations of science. Chemistry, for example, has taught agriculture how to utilize the refuse of slaughter houses and fisheries--the bones, the flesh, the blocd, which but a few years ago were waste, a nuisance and a peril to the public health. It has found vast mines of fossil phosphates in England, Norway, Spain, France, Germany, Russia, in Austria, Canada, and many parts of the United States; and has shown how they may be quickly and profitably converted into a precious fertilizer.

"Chemistry, by discovering and actually defining the food elements of vegetable growth, and by revealing their sources and realizing the means of making them cheaply available to the farmers, has triumphantly overcome one of the previously insuperable obstacles to the development of national wealth.

"Italy, Germany, France, Britain, and the United States have seen or are seeing the productiveness of thousands of their fields decline to a profitless minimum, until lands once beautiful with harvests are desolate and abandoned. But the artificial barrenness and exhaustion, like the natural barrenness of the heath, or sand-down, yields to the touch of science; and in all the older countrics I have named, the work of reclamation is in full progress, and barring some great calamity of politics cr nature, we are confident that the producing power of their soil will never again be less than now, but will increase many fold in the future, until they become gardens in all their breadth and to the very hill-tops.

THE DOCTRINE OF MALTHUS AND THE FOOD SUPPLY OF

THE FUTURE.

This last statement promises wonderful things. It also brings us to the gist of the whole matter.

The doctrine of Malthus regarding the future food supply of the world and the ultimate starvation of a portion of the race, has been greatly misrepresented, but even the most favorable interpretation is a gloomy one. Briefly stated, the theory is that population increases

in a geometrical, and food supply in an arithmetical ratio and hence the time must come when there will not be food enough. Perhaps the simplest and most correct reply to it is that the assumption that the race increases and will continue to increase in a geometrical ratio is not borne out by observed facts. The theory that the food-supply increases in only arithmetical ratio and must ultimately reach its limit is doubtless nearer the truth. But while there is a limit to the possible production of food, it transcends all the ideas that ever occurred to Malthus or to the people of his time. It has always been assumed that the capacity of the soil to produce plants is measured by what is popularly called its fertility; that is to say, the amount of production possible under ordinary conditions of culture. The science of to-day, however, shows this measure to be incorrect, and the practice of agriculture is already beginning to add its testimony. to the same effect. And remarkable as is the story told of fertility in market gardens, the reclaiming of the desert and in irrigation, it is only the first chapter of a tale whose already attested wonders almost rival those of the Arabian Nights.

The fundamental mistake out of which grew the gloomy doctrines of the older theorists was in measuring the possibilities of production by what they knew of soil culture. Science had not revealed to them that, aside from proper temperature and moisture, essential factor in vegetable production is plant food; that this may be given to the plant without the aid of the soil; that what they understood, by soil fertility is a comparatively unessential factor of agricultural production; that in short, the possibilities of the food supply in the future are measureless. Since some of these facts are of comparatively late discovery and not very generally understood and their bearing upon the present question is not always appreciated, they demand, perhaps, a few words of explanation here.

Modern research, in discovering the laws of nutrition and growth of plants, has shown that they can flourish on the most barren soil or even without any soil at all. Of the materiais that make up the plant, only a very small proportion, say two per cent or there

abouts of the weight of grass when ready to be made into hay and a still smaller proportion of the ripened grain of wheat or corn, for instance, has come from the soil, the rest has been supplied by the air from its stores, which are inexhaustible. If we heat

a wisp of hay, a grain of wheat or a piece of potato, in an oven long enough, it will be dried. The water thus driven out came from the air, though the plant obtained most, if not all, of it from the soil its roots.

through

It we put the dried material into the fire, the bulk of it will burn away and only ashes will remain. The combustible portion consists mainly of four chemical elements, carbon, oxygen, hydrogen, and nitrogen. The carbon was obtained by the plant from the air, mainly through its leaves. Oxygen and hydrogen are the constituents of the water, which the air also furnished, and the nitrogen likewise came from the air, though a large part of it (until lately it has been claimed that practically all), was first accumulated in the soil and taken up by the plant roots. The only food which the soil supplies to plants from its original sources is the small quantity of mineral matter which we call ashes when the plant is burned. Of every hundred pounds of the flour we use for bread or the pasture grass from which cattle feed and our meat is made, only a little over a pound in the case of the flour and about two pounds in the case of the grass was furnished by the soil on which the wheat and grass were grown. And that small quantity which the soil contributes from its own original stores is made up of a certain list of chemical elements the majority of which are contained in ordinary soils in such abundance that the cropping of ages would not begin to exhaust them.

It is hard to think of anything more barren, more destitute of fertility, than sea-sand. In connection with some studies of the chemistry of vegetable production in the laboratory of Wesleyan University, we have been growing plants in just such sand, brought from the shore of Long Island Sound. To divest it of every possible trace of material which the plants might use for food except, the sand itself, it was care

fully washed with water and then heated. The young man who prepared the sand for use, in his zeal to burn out the last vestiges of extraneous matter, heated the iron pots in which it was calcined so hot that they almost melted. The sand was put in glass jars, water was added, and minute quantities of chemical salts, which plants take from the soil, were dissolved in it. In the sand thus watered and fertilized, dwarf peas were grown. Peas of the same kind were culti vated by a skillful gardener in the rich soil of a gar den close by and grew to a height of about four feet, while those in the sand with the water and the mi. nute quantities of chemical salts reached a height of eight feet.

This is an old story. For that matter, plants will thrive without even the sand. Experimenters have devised the method of water-culture, by which plants are grown, not in soil at all, but with their roots immersed in water in which are dissolved the ingredients of their food which the roots ordinarily gather from the soil. The stems and branches are upheld by ap propriate supports. Thus cultivated, they are in every way healthy and attain a more than tropical luxuriance, a development rarely equaled in field culture. This method of growing plants by water culture, as it is called, has been developed in Germany more than anywhere else. Professor Wolff, of the Agricultural Experiment Station in Hohenheim, raised four oat plants in this way with 46 stems and 1,335 well-developed seeds. Professor Nobbe, of the Experiment Station in Tharand, thus grew in jars of water a Japanese buckwheat plant, nine feet high, weighing, when airdry, 4,786 fold as much as the seed from which it was produced and bearing 796 ripe and 108 imperfect seeds. Wheat, maize and other plants, and even trees, are grown in this way. Professor Nobbe now has some trees produced by water culture from seeds of others which also had never been in soil at all, but had grown with their roots immersed in water. The requisites for such plant growth are proper temperature, water, and certain elements of plant-food, of which very minute quantities suffice. Given these and the air will supply the rest, and if other conditions are right, abundant yield will be sure.

The experimenters have found just what are the chemical elements that plants take up by their roots. The list includes phosphoric acid, sulphuric acid, chlorine, iron, lime, magnesia, potash, and, for many plants, at any rate, some compounds of nitrogen. It transpires that the most of these substances exist in abundance in even the most barren soils. Iron and chlorine never, magnesia rarely, and the sulphuric acid and lime seldom fail to be supplied in abundance. The elements most frequently lacking in our ordinary soils are phosphorus which is contained in phosphoric acid; potassium, the basis of potash; and nitrogen. These soil elements are quickest exhausted in our ordinary way of farming; it is they more than any other that are wanting in worn out land, and they are the most precious constituents of manure. With plenty of them and proper water supply, we need have no fear for the agriculture or the world's food-supply of the future.

Although it has been reserved for the science of the present to show that warmth, water and plant food are the prime factors of successful crop-growing, the principle has been acted upon from time immemorial. It is at the basis of the irrigation that has been practiced since the most ancient times. It is actually applied in market gardens about Paris, where such surprising results are obtained; on the sands of Belgium and Holland, that yield food for a dense population, and on the soils of North Germany, which, though they are naturally poor, and have been in cultivation for many centuries, excel to-day the rich soils of our new West in their produce. Not the natural fertility of the soil, but its rational culture, is what brings the largest, the surest, the most enduring har

vests.

THE FUTURE SUPPLY OF PLANT FOOD.

But can we obtain the phosphoric acid, the potash and the nitrogen?. It seems to be a law of human progress that when a great want is defined, the discovery of its supply soon follows. When advancing science had revealed the need of phosphoric acid in poor and exhausted soils, mines of phosphate were