Comment by TeMPOraL

Apples and apple seeds to me. The way I see it, the thermostat contains the motor (EDIT deleted the rest of explanation).

EDIT: the way I see it, talking about gradients here is nonsense. The wax motor works by expansion/contraction due to point temperature. No gradient is involved. Gradients are thermostat-level thinking, and even then, in the greenhouse scenario, there is no gradient to talk about, because the whole point is just to vent the heat from inside to outside when inside crosses certain absolute value of T, and the only "gradient" that matters is the assumption that outside side is less than T at all times.