1203. The parts of the corolla range in an alternating manner with those of the calyx, because they are the next supra-consecutive bud.
1204. In accordance with the three stages of the leaf-formation the corolla is also resolvable into three forms. The scale-or root-leaf returns in the several squamiform micropetals of what have been called the Apetalous plants; it corresponds to the involucrum--squamoid corolla. The spathe-or stalk-leaf appears in the tubular-shaped or Monopetalous corolla. It is a leaf-bud, which has only ruptured at the apex, like most calyces, unto which it corresponds--spathoid corolla. Lastly, in the polypetalous corolla the reticular or petiolated leaf appears upon its highest stage--reticular or phylloid corolla. The rank of the leaves consequently determines also that of corollæ.
1205. Although we regard the corolla as a whorl of leaves, namely, as several leaf-buds approximated, a yet clearer insight into its numbers and positional relations is attained, by viewing it only as the lobes of a single leaf.
1206. If we regard the petals of a polypetalous corolla in the import or light of _pinnate leaflets_, the legitimate regularity of their numerical relations, and the so-called irregularity of their arrangement is easily explained. The papilionaceous corollæ have been manifestly constructed according to the plan of the pinnate leaf; the vexillum or vane corresponds to the odd leaflet, the alæ or wings to the two anterior, the carina or keel to the two posterior pinnate leaflets; and hence their consecutive ratio of decrease in respect to size.
1207. All irregular corollæ admit of being referred to the papilionaceous form. One petal is always found, which separates from the others, is either larger or smaller, or entirely ablated, and consequently corresponds to the odd pinnate leaflet or vane.
1208. The irregular monopetalous or tubular corollæ admit also of being referred to the papilionaceous form. They need only be regarded as a confluence of petals. The labiate corollæ are one of the same character; but, on the contrary, the lower lip is trifid, the upper, and thus the keel, bifid. Here the papilionaceous corolla stands, properly speaking, reversed.