Opposed to the absorption of carbon dioxide and the breathing out of oxygen, which is really a digestive operation, the plants, queerly enough, carry on a directly opposite process which involves the absorption of oxygen and the breathing out of carbon dioxide. This is a respiratory process akin to breathing in animals. It is carried on in such a relatively small way that it does not seriously affect the statement that “plants breathe in carbon dioxide and breathe out oxygen” and so are purifiers of the air which man and animals contaminate. Besides this general use of gases common to nearly all plants, a few of the members of the vegetable world specialize in the production of protective and poisonous vapours of various composition. One of the most interesting of these is the Gas Plant of the South American jungles. This beautiful white-flowered inhabitant of the tropics is entirely protected from leaf-destroying insects and birds by the poisonous vapours it constantly pours forth. The plants are expert chemists, and the reactions in which they engage are, on the whole, much simpler than those which go on in the bodies of animals. Vegetable tissue is largely carbon, hydrogen, oxygen and nitrogen. It is a curious fact that instead of using the abundant carbon compounds present in decomposed animal and vegetable matter of the soil the plants get most of their carbon from the carbon dioxide of the air. Inversely, they largely disregard the seventy-eight per cent nitrogen of the air, and extract that element from the complicated compounds found in the soil, or take it from the air only by aid of certain Bacteria. Certain plants manufacture lime and metallic oxides with which to harden the protective armour they wear. Many others generate nitric acid, carbonic acid and ammonia for use in their interior laboratories. Roots nearly always secrete a fluid which aids in the absorption of minerals from the earth. It is so powerful that quartz, flint and limestone are often scratched and corroded by its action. Above and below ground, plants are active chemical laboratories. The differences of taste, smell and colour which characterize leaves, blossoms and fruits are due to the presence of various organic compounds. These are largely volatile oils which are more complex than the substances involved in the simpler life processes. The slow or rapid evaporation of these oils influences the strength and character of an odour. When a flower or fruit passes through infinite gradations of colour, we can give no adequate account of the chemical changes involved. All we can do is to observe and to note. Sometimes infusions of iron sulphate or other chemicals in the soil darken the hues of flowers. Gardeners profit by this fact in the cultivation of certain varieties of Hortensia.