This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The number of parts forming the calyx varies, but four (as in the Wallflower) and five (as in the Buttercup) are extremely common numbers. These parts are situated on the outside of the flower proper, and when free from one another are termed sepals; but when more or less united they are described as the segments, lobes, or teeth of the calyx, according to the length of the free portion. Usually they are small, green, and serve to protect the other parts of the flower. In the Christmas Rose (Helleborus niger), Marsh Marigold (Caltha), Delphinium, and Aconi-tum they are large, highly coloured, showy, and perform the function of the corolla in attracting insects.