277. The pieces of the calyx or the corolla either overlap each other in the bud, or they do not. When they do not overlap, the æstivation is _Valvate_, when the pieces meet each other by their abrupt edges, without any infolding or overlapping; as the calyx of the Linden or Basswood (Fig. 277). [Illustration: Fig. 277. Diagram of a flower of Linden, showing the calyx valvate and corolla imbricate in the bud, etc.] _Induplicate_, which is valvate with the margins of each piece projecting inwards, as in the calyx of a common Virgin's-bower, Fig. 278, or [Illustration: Fig. 278. Valvate-induplicate æstivation of calyx of common Virgin's-bower.] _Involute_, which is the same but the margins rolled inward, as in most of the large-flowered species of Clematis, Fig. 279. [Illustration: Fig. 279. Valvate-involute æstivation of same in Vine-bower, Clematis Vitialla.] _Reduplicate_, a rarer modification of valvate, is similar but with margins projecting outward. _Open_, the parts not touching in the bud, as the calyx of Mignonette. 278. When the pieces overlap in the bud, it is in one of two ways; either every piece has one edge in and one edge out, or some pieces are wholly outside and others wholly inside. In the first case the æstivation is _Convolute_, also named _Contorted_ or _Twisted_, as in Fig. 280, a cross-section of a corolla very strongly thus convolute or rolled up together, and in the corolla of a Flax-flower (Fig. 281), where the petals only moderately overlap in this way. Here one edge of every petal covers the next before it, while its other edge is covered by the next behind it. The other mode is the [Illustration: Fig. 280. Convolute æstivation, as in the corolla-lobes of Oleander.] [Illustration: Fig. 281. Diagram of a Flax-flower; calyx imbricated and corolla convolute in the bud.] _Imbricate_ or _Imbricated_, in which the outer parts cover or overlap the inner so as to "break joints," like tiles or shingles on a roof; whence the name. When the parts are three, the first or outermost is wholly external, the third wholly internal, the second has one margin covered by the first while the other overlaps the third or innermost piece: this is the arrangement of alternate three-ranked leaves (187). When there are five pieces, as in the corolla of Fig. 225, and calyx of Fig. 281, as also of Fig. 241, 276, two are external, two are internal, and one (the third in the spiral) has one edge covered by the outermost, while its other edge covers the innermost; which is just the five-ranked arrangement of alternate leaves (188). When the pieces are four, two are outer and two are inner; which answers to the arrangement of opposite leaves. 279. The imbricate and the convolute modes sometimes vary one into the other, especially in the corolla. 280. In a gamopetalous corolla or gamosepalous calyx, the shape of the tube in the bud may sometimes be noticeable. It may be