ESTIVATION OR PR^HFLORATION. 273 



mon enough in the corolla. When this obliquity of position is strong, 

 the petals themselves are usually oblique, or unequal-sided, from the 

 lesser growth of the overlapped side. This is well seen in the pet- 

 als of most Malvaceous plants, and in those of the St. Johnswort. In 

 the Pink, however, and in many other instances, the petals are 

 symmetrical, although strongly convolute in aestivation. When the 

 petals are broad, this convolute arrangement is frequently conspicu- 

 ous in the fully expanded flower, as well as in the bud. The con- 

 volution in the bud is often so great, that the petals appear as if 

 strongly twisted or rolled up together, each being almost completely 

 ' overlapped by the preceding, so that they become convolute nearly 

 in the sense in which the term is used in vernation ; as in the Wall- 

 flower (Fig. 441, 442). Although there is some diversity of usage, 

 the terms convolute and contorted in aestivation are now for the most 

 part employed interchangeably, or nearly so. 



499. The valvular or valvate asstivation is that in which the pai-ts 

 of a floral circle are placed in contact, edge to edge, throughout their 

 whole length, without any overlapping, as in the calyx of the Mal- 

 low and Linden, Fig. 440. Here the members of the circle stand in 

 an exact circle, no one being in the least degree lower or exterior. 

 The edges of the sepals or petals in this case are generally abrupt, 

 or as thick as the rest of the organ ; by which mark the valvate ajs- 

 tivation may commonly be recognized in the expanded flower. 



500. By inflexion of the edges, the valvate a3stivation passes by 

 gradations into the induplicate (Fig. 

 445), and this, when the margins are in- 

 rolled, into the involute (Fig. 446), as is 

 exemplified by the calyx of different spe- 

 cies of Clematis. On the other hand, the 

 valvate calyx of many Malvaceous plants 

 has the margins projecting outwards into salient ridges, or is redupli- 

 cate, in aestivation. 



501. In the Mignonette, and some other flowers, the ajstivation is 

 open ; that is, the calyx and corolla are not closed at all over the 

 other pai'ts of the flower in the bud. 



502. The form of the tube of the calyx or corolla in the bud 

 sometimes has to be considered. Sometimes it is plicate, or plaited 

 lengthwise ; and the plaits may be turned either inwards, as in the 



FIG, 445. Diagram of the valvate-iuduplieate wstivation of the calyx of Clematis Virgini- 

 ana. 446. Same of Clematis Viticella, the margins involute. 



