In the living organism nutrition results in growth, development, and evolution. Growth and development also follow the absorption and fixation of aliment by an osmotic production. An osmotic production grows, its form develops and becomes more complicated, and its weight increases. An osmotic growth may weigh many hundred times as much as the mineral sown in the solution, the mother liquor losing a {151} corresponding weight. Thus growth, which has hitherto been considered an essential phenomenon of life, is also a phenomenon common to all osmotic productions. Osmotic growths like living things may be said to have an evolutionary existence, the analogy holding good down to the smallest detail. In their early youth, at the beginning of life, the phenomena of exchange, of growth, and of organization are very intense. As they grow older, these exchanges gradually slow down, and growth is arrested. With age the exchanges still continue, but more slowly, and these then gradually fail and are finally completely arrested. The osmotic growth is dead, and little by little it decays, losing its structure and its form. The membranes of an osmotic growth thicken with age, and thus oppose to the osmotic exchanges a steadily increasing resistance. Young osmotic cells appear swollen and turgescent, whereas old ones become flaccid, relaxed, and wrinkled. Analogous phenomena are met with in living organisms, the calcareous infiltration of the vessels representing the thickening and hardening of the osmotic membranes. The plumpness of a child and the turgescence of young cells are but the expression of high osmotic tension, while relaxation and flaccidity of the tissues in old age betrays the fall of osmotic pressure in the intracellular tissues. Circulation of the nutrient fluid may also be observed in an osmotic growth as in a living organism. If we take a calcareous growth with long ramified stems and dilute the mother liquor considerably, we may see currents of liquid issuing from the summit of the growth--currents which are made visible by the cloudy precipitates which they cause. The same current is also rendered visible in the stems themselves by the motion of the granulations and gas bubbles in the interior of the osmotic cells. It is plain that some such circulation must exist, for how could a membrane be formed 30 centimetres from the seed if the membranogenous substance did not circulate through the stem? A moment's consideration will show that the propulsion is due to osmotic pressure and not to mere differences of density, for the liquid {152} which rises in the stem is a concentrated solution of calcium salt much denser than the mother liquor, and the current of liquid after rising in the stem may be seen to fall back again through the liquid. [Illustration: FIG. 61.--A group of osmotic forms.]