AESTIVATION. 



283 



torted sestivation is scarcely ever met with in the calyx, but is very 

 common 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, which is by no means so 

 favorably situated in this respect as is the free external portion, 

 a case of partial obliteration or dwarfing from pressure. This is 

 well seen in the petals of most Malvaceous plants, to some extent in 

 those of Geranium, Flax, and Wood-Sorrel, and strikingly in those 

 of the St. John's-wort, and in the lobes of the corolla of the Peri- 

 winkle (Vinca) and of most other Apocynaceous plants. In the 

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

 metrical, although strongly convolute in sestivation. When the 

 petals are broad, this arrangement is frequently conspicuous in the 

 fully expanded flower, as well as in the bud (as in Fig. 365). The 

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

 strongly twisted or rolled up together, each being almost complete- 

 ly overlapped by the preceding, so that they become convolute 

 nearly in the sense in which the term is used in vernation ; as in 

 the Wallflower (Fig. 360, 361). Although there is some diver- 

 sity of usage, the terms convolute and contorted in sestivation are 



now for the most part employed interchangeably, or nearly so. In 



FIG. 355- 363. Diagrams of aestivation. (When there are two circles, the outer represents 

 the calyx and the inner the corolla.) 355. Valvate. 356. Valvate calyx; the corolla indu- 

 plicate or nearly conduplicate. 357. Involute, rather than induplicate, sepals of Clematis. 

 358. Quincuncially imbricated; the first leaf on the upper side. 359. Vexillary imbricated 

 papilionaceous corolla. 360. Imbricated calyx of Wallflower (two outer and two inner sepals), 

 and within the strongly contorted or convolute corolla. 361. Contorted or convolute corolla, 

 with the petals more expanded. 362. Plaited tube of the corolla of Campanula. 363. Plaited 

 and supervolute corolla of Convolvulus. 



