The chemical activities of plants are of incalculable value to man. They change air, water and mineral salts into forms easily assimilable by the human system. Eliminate all the vegetable life from this planet, and the animals, including man, would perish in a few months. Man has also learned to make abundant use of plant substances for innumerable purposes. Potash is an example of how the plants come to our aid in furnishing us a valuable chemical. It is extracted from wood, Seaweed and Banana stalks. These plants have discovered a way of getting it out of its well-nigh insoluble earth combinations with silica. If it had not been for certain industrious sea plants, man would probably never have been aware of the important chemical twins, bromine and iodine, so important in photography. These plants patiently filter them out of sea water where they exist in microscopic quantities, and build them into their bodies. Beer is possible because germinating grains transform amylum or plant starch into sugar. We find ripe fruits palatable because their acids change into sugar under the influence of sunlight. Man seems to have outstripped the plants in the use of light, heat, electricity, and other physical forces, but the plants have more engineers among them than we imagine. In the fact that man has just learned to extract nitrogen from the air by the agency of electrical discharges, lies the probable explanation of how the plants have been doing the same thing for years. It is believed that the minute electrical discharges continually going on between the different air strata make small quantities of nitrogen assimilable for the plants. The micro-organisms which also furnish nitrogenous material to the plants may get nitrogen from the air in the same way. It is quite certain that the plants are affected by the chemical state of the atmosphere. Everyone knows what an important part light plays in plant physiology, but the fact that certain plants produce their own lights, while generally known, is not universally understood. The Austrian naturalist, Heller, was the first to demonstrate that the glowing of decayed wood at night is caused by emanations of light from Fungus growing in the cavities. A similiar organism called Luminous Peridineas (sometimes classed as an animal) is responsible for the phosphorescence of the ocean and the night lights of many flowers.