If you've ever noticed how sunflowers follow the sun each day from sunrise to sunset, then you've witnessed the phenomenon called "floral heliotropism." Also called "phototropism," this amazing ability of some plants to actually follow the sun's path is not the plant's adoration and worship of the sun (as those who believe in the secret life of plants might conclude), but rather a structural motor ability of a particular part of the plant's stem just beneath the flower. This bendable part is called a pulvinus which is defined as "a cushion-like swelling at the base of the stalk of a leaf or leaflet" (Random House Dictionary, 2009). At the botanical level, in reaction to the light of the sun, plant cells in the pulvinus actually draw, concentrate and redistribute potassium ions from one segment of the pulvinus to another. This changes the cell wall pressure. The result is slow, motor movement of the sunflower's head.

Interestingly, ancient Roman philosophers and religious thinkers used the term, pulvinus, to describe "a cushioned couch kept in readiness for any visitation of a god." For the sunflower -- and for those who do believe in the secret life of plants -- that god would be the Sun.