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What makes the sunflower such a puzzle is that it belongs to a group of flowers that lack what is known as a pulvinus—a thickening at the base of a leaf or other structure that changes its rigidity in response to light.

As the sun moves across the sky, different amounts of water flow into different parts of the pulvinus, nudging the leaf in the sunniest direction.

The pulvinus of this capital is ornamented with leaves, as 263 in the example from Athens in B�tticher's Tektonik, pl.

It was not a column, it was a pulvinus, or volute, of a colossal marble altar, worthy of being compared, in size and perfection of work, with the Altar of Peace discovered under the Palazzo Fiano, with that of the Antonines discovered under the Monte Citorio, and with other such monumental structures.

Oxalis.—We now come to cotyledons provided with a pulvinus, all of which are remarkable from the continuance of the nocturnal movements during several days or even weeks, and apparently after growth has ceased.