THE RESPLENDENT COROLLA 127 
the flower opens (e.g., Poppy), or wither as the petals 
wither, or remain fresh until the fruit is ripe. Some- 
times, as in many Ranunculaceze (compare Anemone, 
Caltha, Helleborus), they take on the advertising role 
usually assigned to the petals, being large and col- 
oured, while the petals themselves are minute. In 
the Monocotyledons they usually join with the petals 
in adorning the flower. The next whorl, lying inside 
(that is, above) the sepals, is formed of petals, con- 
stituting the corolla. The connection of colour and 
form of petals with the visits of insects, and their 
relative insignificance in wind-pollinated flowers, has 
already been referred to (p. 81). The marvellous 
variety of colour and form observable in the corolla 
has for its main object the attracting of insects to the 
flower. The petals have departed much farther from 
the ordinary leaf-form than the sepals. They assume 
brilliant hues of every tint, the pigment being due 
either to colouring matter dissolved in the cell-sap 
(pinks and blues) or to small coloured solid bodies 
(chromoplasts) contained in the cells (reds and yel- 
lows). Chlorophyll being absent, the coloured petals 
do not assist assimilation: they are purely advertise- 
ments, though incidentally they often fulfil a useful 
protective role for the important organs which they 
surround. In this latter connection their sensitive- 
ness to changes of light and temperature, which 
causes them to close in dark or cold weather, is a 
very familiar phenomenon; as is also the excellent 
protection which they provide in flowers such as those 
of the Labiate, where, fused together into a tube, 
they form a kind of cave in which the stamens and 
pistil nestle securely. 
