VARIETIES OF IMBRICATED ASTIVATION, 221 
lapping one of the internal by one margin, while it is itself 
overlapped on its other margin by one of the external parts, 
the xstivation is said to be qwincuncial (fig. 450). Familiar 
examples of this form are afforded by the corolla of the Rose, 
and the calyx of the Bindweed (Calystegia sepiwm). In this 
kind of zestivation the spiral arrangement of the parts is well 
seen, and is indicated in the diagram (fig. 450) by a dotted 
line. The spiral cycle thus formed, which is the normal 
one in pentamerous or quinary flowers (those with the parts 
in fives), and which occurs in the majority of Dicotyledons, 
corresponds to the =, pentastichows, or five-ranked arrangement 
of leaves. When in a quincuncial arrangement the second part 
of the cycle becomes wholly internal instead of being external, 
the regularity of the quincunx is interrupted, and a variety of 
wstivation occurs to which the name cochlear has been given 
Fia. 449. Fia. 450. Fie. 451. Fic. 452. 
aN 
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Fig. 449. Diagram to illustrate imbricate estivation. The figures 1, 2, 3, 4, 
5, Show that the successive parts are arranged ina spiral manner.— Fig. 
450. Diagram to illustrate quincuncial eestivation. 1 and 2 are external, 
4 and 6 internal, and 3 is partly external and partly internal§@ Fig. 451. 
Diagram to illustrate cochlear estivation. The part marked 2 in the 
preceding diagram is here wholly internal instead of external as in the 
quincuncial arrangement. The dotted line marked 2 indicates itsnormal 
position in the true quincuncial variety of zestivation. Fig.452, Diagram 
to illustrate vexillary zstivation. 1 and 2 form the ale or wings, 3 and 
5 the carina or keel, 4 the vexillum. (See Papilionaceous Corolla.) 
(fig. 451). Familiar examples of this are afforded by the Snap- 
dragon (Antirrhinum majus), and other allied plants. Another 
marked modification of imbricated ezstivation occurs in the 
corolla of the Pea and other allied plants, where the superior 
petal 4, which is generally the largest, and called the vexillum, 
is folded over the others which are arranged face to face (fig. 
452). This kind of estivation is commonly termed vewillary. 
It frequently happens that the calyx and corolla exhibit 
different kinds of estivation. Thus, in Guazwma ulmifolia the 
calyx is valvate ; and the corolla induplicate. In Malvaceous 
plants the calyx is valvate or some form of circular estivation ; 
and the corolla twisted. In these two examples the different 
varieties of zstivation, as exhibited by the two floral envelopes, 
may be considered to belong to the same class of sestivation, i.e. 
the circular. But instances also frequently occur where the 
calyx and corolla present different modifications, and which 
belong to both classes ; thus, in the Corn Cockle (Githago segetum), 
