A bibliography of the most important works on the subject will be found in Physiological Botany, page 351, note.] [Footnote 2: Reader in Botany. XV. Insectivorous Plants.] 5. _Respiration_.--Try the following experiment in germination. Place some seeds on a sponge under an air-tight glass. Will they grow? What causes them to mould? Seeds will not germinate without free access of air. They must have free oxygen to breathe, as must every living thing. We know that an animal breathes in oxygen, that the oxygen unites with particles of carbon within the body and that the resulting carbonic acid gas is exhaled.[1] The same process goes on in plants, but it was until recently entirely unknown, because it was completely masked during the daytime by the process of assimilation, which causes carbonic acid to be inhaled and decomposed, and oxygen to be exhaled.[2] In the night time the plants are not assimilating and the process of breathing is not covered up. It has, therefore, long been known that carbonic acid gas is given off at night. The amount, however, is so small that it could not injure the air of the room, as is popularly supposed. Respiration takes place principally through the stomata of the leaves.[3] We often see plants killed by the wayside dust, and we all know that on this account it is very difficult to make a hedge grow well by a dusty road. The dust chokes up the breathing pores of the leaves, interfering with the action of the plant. It is suffocated. The oxygen absorbed decomposes starch, or some other food product of the plant, and carbonic acid gas and water are formed. It is a process of slow combustion.[4] The energy set free is expended in growth, that is, in the formation of new cells, and the increase in size of the old ones, and in the various movements of the plant. [Footnote 1: See page 13.] [Footnote 2: This table illustrates the differences between the processes. ASSIMILATION PROPER. RESPIRATION. Takes place only in cells Takes place in all active cells. containing chlorophyll. Requires light. Can proceed in darkness. Carbonic acid absorbed, Oxygen absorbed, carbonic oxygen set free. acid set free. Carbohydrates formed. Carbohydrates consumed. Energy of motion becomes Energy of position becomes energy of position. energy of motion. The plant gains in dry The plant loses dry weight. weight. Physiological Botany, page 356.] [Transcriber's Note: Two footnote marks [3] and [4] above in original text, but no footnote text was found in the book]