In Cycas whorls of scales alternate with large pinnate leaves.
There are con siderable irregularities, how ever, in this respect, and the number of leaves in different whorls is not always uniform, as may be seen in Lysimachia
Of these whorls the two internal, forming the sporophylls, constitute the essential organs of reproduction; the two outer whorls are the protective coverings or floral envelopes.
2) the upper whorls are capitate, the lower filiform.
In plants, as Nymphaea alba, where a spiral arrangement of the floral leaves occurs, it is not easy to say where the calyx ends and the corolla begins, as these two whorls pass insensibly into each other.