14. The different combinations of the elements for the formation of mineral, vegetable and animal substances can then be formed only under propitious circumstances. Outside of these circumstances the elementary principles are in a sort of inertia; but, as soon as conditions are favorable, a work of elaboration commences. The molecules begin to move: they act, approach, and are drawn toward one another, and separate by virtue of the law of affinity, and by their multiple combinations compose the infinite variety of substances. If these conditions cease, the work is suddenly arrested, to recommence so soon as conditions are again furnished. Thus vegetation is active, retards, ceases, and resumes action under the power of heat, light, humidity, cold, and dryness; as some plants prosper in one climate or soil, and perish in another.