Fig. 2.

Closing of a flower of Ipomoea purpurea, the morning glory. Images a–d show this process. As in many species, the flower does not close passively by wilting, but by a complex process. In I. purpurea, the petal midribs perform differential growth, leading to curling up of the petals until the flower is closed. While opening of flowers allows pollination, the functional background of closing is more obscure. Please note that the images are not to scale, because the diameter of the flower decreases during closing. Note also that the color of the petals changes during closing