Page:Popular Science Monthly Volume 30.djvu/299

Rh which the following conclusions were drawn: 1. The combined nitrogen, which is the product of vegetable and organic life, forms the chief source of nitrogen for the growing plant. 2. Before it is assimilated by the plant, it undergoes a process of oxidation which is due solely to a living organism. 3. The nitrates thus formed are absorbed by the plant, and the albuminoids of the new growth are formed from the nitric nitrogen by a process of reduction. The nitrates themselves are subject to the action of a ferment by which a deoxidation takes place, and free nitrogen and nitrous oxide are evolved. 4. The diminution in the quantity of available nitrogen thus supplied is restored by the fixation of free nitrogen, by the action of organisms in the soil, or by the oxidation of free nitrogen by the interior cells of the plant acting in a manner analogous to the nitric ferment in the soil, or by the oxidation of free nitrogen by electrical discharges or by combustion. 5. The quantity of combined nitrogen brought to the soil and growing plant by the rain-water and the atmosphere, arising from the last two phenomena, is an inconsiderable amount when compared with the whole weight required by the crop. Concerning the future food-supply, Professor Wiley said: "Since, with a proper economy, the natural supplies of potash and phosphoric acid may be made to do duty over and over again, and last indefinitely, the economist, who looks to the welfare of the future, need have no fear of the failure of these resources of the growing plant. Indeed, it may be said that the available quantities of these may be increased by a wide practice of agriculture based on the teachings of agricultural chemistry. But with the increase of population comes an increased demand for food, and therefore the stores of available nitrogen must be enlarged to supply the demands of the increased agricultural product. It is certain that with the new analytical methods, and the question raised by the investigations, many series of experiments will be undertaken, the outcome of which will definitely settle the question of the entrance of free nitrogen into vegetable tissues. If this question be answered affirmatively, agricultural science will not place bounds to the possible production of foods. If the nitrifying process goes on within the cells of plants, and if living organisms do fix free nitrogen on the soil in a form in which at least a portion of it may be nitrified, we may look to see the quantities of combined nitrogen increased pari passu with the needs of plant-life. Thus, even intensive culture may leave the gardens and spread over the fields, and the quantities of food suitable for the sustenance of the human race be enormously increased."

Evolution of Means of Defense.—Mr. Charles Morris, in a paper of the Academy of Natural Sciences of Philadelphia, on "Attack and Defense as Agents in Evolution," suggests that the various modifications which are seen in the hard parts of animals at different periods indicate adaptation to dominant ideas that have different relations to the prevailing conditions of existence of the time. The earliest animals were probably wholly soft, and have left no remains except an occasional track on the mud of their day. Then came in armored forms with external shells. Swift-swimming armored animals came in with the fishes, and seem to have increased in thickness and weight of armor to the end of the Devonian era. "If, now, we come down to a later era of life, we find in operation what seems a third idea of Nature. The prevailing tendency in animal life is no longer to assume armor, but to throw off armor, and return toward the unprotected condition. The causes of these changes are related to the development of weapons of assault in attacking animals, and to the kind of defense that was most available and useful, or most efficient at the period. As Mr. Morris says: "In the primeval epoch it is probable that only soft-bodied animals existed, and the weapons of assault were the tentacles, the thread-cell, the sucking-disk, and the like unindurated weapons. At a later period armor became generally adapted for defense, and the tooth became the most efficient weapon of attack. Still later, armor was discarded, and flight or concealment became the main method of escape, and swift pursuit the principle of attack, while claws wore added to teeth as assailing weapons. Finally, mentality came into play, intelligence became the most efficient