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182 the source of this organic matter, either or both of which may be correct: First. There seems to be no doubt that most plants, especially those grown in soils rich in humus, take up a portion of their food in the form of semi-organic matter, or soluble humus. The combustion of a portion of this in every part of the plant, by means of oxygen also absorbed by the roots, and the formation of CO2, undoubtedly creates a supply of force night and day, independently of sunlight. The force thus produced by the combustion of a portion might be used to raise the remainder into starch, dextrine, etc., or might be used in tissue-building. During the day, the CO2 thus produced would be again decomposed in the leaves by sunlight, and thus create an additional supply of force. During the night, the CO2 would be exhaled.

Again: It is possible that more organic matter is made by sunlight during the day than is used up in tissue-building. Some of this excess is again consumed, and forms CO2 and H2O, in order to continue the tissue-building process during the night. Thus the plant during the day stores up sun-force sufficient to do its work during the night. It has been suggested by Dr. J. C. Draper, though not proved, or even rendered probable,