220 VARIETIES OF CIRCULAR ZXSTIVATION. 
of its component parts being slightly thickened, or at all events 
not thinner than the rest of the organ: whereas in all varieties 
of imbricated or spiral zstivation, the overlapping margins are 
usually thinner, as may be well seen in the sepals of the species 
of Geranium. When the component sepals, or petals, instead of 
being flattened, are folded inwards at the points where they 
come in contact (fig. 446), the ezstivation is induplicate, as in 
the petals of Guazwma wlmifolia, and in the sepals of some 
species of Clematis. When the margins are turned outwards 
under the same circumstances (jig. 447), the ezstivation is re- 
duplicate, as in the sepals of the Hollyhock (Althea rosea), and 
some other Malvaceous plants ; and in the petals of the Potato. 
When the parts of a whorl are placed at the same height, or 
apparently so, as in the ordinary forms of circular estivation, 
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. 448), the ezstivation is contorted or 
twisted. -It occurs very frequently in the corolla, but is very 
rare in the calyx. Examples may be seen in the corolla of the 
Hollyhock and other Malvaceous plants ; in that of the common 
Flax (Linum usitatissimum), and generally in the order Linacee ; 
in the St. John’s Wort (Hypericum) ; in the Periwinkle (Vinca), 
and in many other plants of the order Apocynacez, to which 
this plant belongs. Twisted zestivation may be regarded as 
intermediate between the circular and imbricated forms. 
When in this variety of estivation the component organs 
become united, they may be variously plaited or plicate, as in 
the corolla of the common Bindweed and of other Convolvu- 
laceze, in which case the zstivation is usually termed plicate or 
plaited. 
2. Varieties of Imbricated or Spiral AAstivation.—We distin- 
guish five varieties of this kind of estivation, i.e., the imbri- 
cate, convolute or enveloping, quincuncial, cochlear, and vexillary. 
The true imbricate zstivation, as seen for instance in the calyx 
of Camellia japonica (fig. 449), is formed by the component 
parts being placed at different levels, and overlapping each 
other more or less by their margins like the tiles on the roof of 
a house, the whole forming a spiral arrangement ; this is a very 
common variety. When the parts, instead of merely overlap- 
ping, completely envelope each other, as in those of the calyx of 
Magnolia grandiflora, and in those of the corolla of Camellia japo- 
nica, the wstivation is termed convolute by some botanists ; but 
this term is now more frequently applied to the contorted variety 
of estivation, when the parts overlap to a considerable degree, 
as in the Wallflower. When the parts of a floral whorl are five 
in number, and these arranged in such a manner that there are 
two parts placed on the outside, two inside, and the fifth over- 
