ORGANS OF REPRODUCTION. 



219 



duplicative, as in the calyx of Althcea rosea, and some other 

 Malvaceous Plants, and in the corolla of the Potato. 



When the parts of a whorl are at the same height, or ap- 

 parently so, as in the ordinary forms of circular aestivation, 

 and one margin of each part is directed obliquely inwards, and 

 is overlapped by the part adjacent on that side, while the other 

 margin covers the corresponding margin of the adjoining part 

 on the other side, so that the whole presents a more or less 

 twisted appearance {fig. 433), the testivation is contorted or 

 twisted. This form may be considered as intermediate between 

 the Circular and Imbricated forms of estivation. It occurs 

 very frequently in the corolla, but is very rare in the calyx. 

 Examples may be seen in the coroUa of Althcea rosea, and other 

 Malvaceous Plants ; in that of the common Flax {Linum), and 

 generally in the order Linacese ; in the Cyclamen ; in the St. 

 John's Wort {Hypericum) ; in the Periwinkle {Vinca), and in 

 many other plants of the same order. 



Fig. 433. 



Fig. 434. 



Fig. 435. Fig. 436. 



Fig. 433. Diagram to illustrate contorted or twisted aestivation. Fig. 434. 



Diagram to illustrate imbricate aestivation. The figures 1, 2, 3, 4, 5, show- 

 that the successive parts are arranged in a spiral manner. Fig. 435 



Diagram to illustrate quincuncial aestivation. 1 and 2 are external, 4 and 



5 internal, and 3 is partly external and partly internal. Fig. 436. 



Diagram to illustrate cochlear aestivation. The part marked 2 in the pre- 

 ceding diagram is here wholly internal instead of external as in the quin- 

 cuncial arrangement. The dotted line marked 2, indicates its normal 

 IHJsition in the imbricate form of aestivation. 



2. Imbricated, Imhricative, or Spiral Estivation. — We shall 

 describe five forms of this class of aestivation, i.e. the imbricate, 

 convolute or enveloping, quincuncial, cochlear, and vexillary. The 

 true imbricate estivation, as seen for instance in the calyx of 

 Camellia japonica {fig. 434), is formed by' the parts being 

 placed at different levels, and overlapping each other more or 

 less by their margins like the tiles on a house, the whole forming 

 a spiral arrangement. It is a very common form of aestivation. 

 When the parts instead of merely overlapping, completely en- 

 velop each other, as in the calyx of Magnolia grandiflora, and in 

 the corolla of Camellia japonica, the aestivation is termed con- 

 volute by some botanists ; but this term is now more frequently 

 applied to the contorted form of aestivation, when the parts 

 overlap to a considerable degree as in the Wallflower. When 



