In these three successive rhythms of expansion and contraction the plant reveals to us the basic rule of its existence. During each expansion, the active principle of the plant presses forth into visible appearance; during each contraction it withdraws from outer embodiment into what we may describe as a more or less pure state of being. We thus find the spiritual principle of the plant engaged in a kind of breathing rhythm, now appearing, now disappearing, now assuming power over matter, now withdrawing from it again.