8G OEGANOGEAPHY AND GLOSSOLOGY. 



ESTIVATION. 



^Estivation (prcefloratio, cestivatio) is the arrangement of the floral organs in the 

 bud, and is of especial importance in respect of the calyx and corolla. 



The leaves of each floral whorl may be inserted exactly at the same level 

 (forming a true whorl), or at unequal heights, when they form a depressed spiral, 

 the lowest leaf of which is necessarily the outermost. The true whorl presents two 

 modes of aestivation the valvate and the contorted. 



1. ^Estivation is valvate (<e. valvaris) when the contiguous edges of the parts touch 

 throughout their length, like the two leaves of a door (460 a) ; and it is then nearly 

 always regular. It is induplicative (OP. induplicativa) when the contiguous parts cohere 

 by a part of their back ; reduplicative (ce. reduplientiva) when by a part of their faces 



460o. Yalvate 4606. Valvat* 461. Valvata 462. Contorted 463. Imhrirate 



icetivation. induplicutive activation. reduplicative [estivation. salivation. motivation. 



(fig. 401). 2. ^Estivation is twisted or contorted 1 (contorta) when the leaves are so 

 placed that each leaf partially covers one of the two between which it is placed, and 

 is similarly covered by the other, as if each were twisted on its axis (fig. 462) ; in 

 this case the whorl is always regular. 



The depressed spiral presents two modes of aestivation : the imbricate, properly 



so called, and the quincunxial. These two are often indifferently termed imbricate. 



1. In the true imbricate aestivation (re. imbricativa, fig. 468) the parts (usually five) 



successively overlap, from the first, which is wholly exterior, to the last, which is 



wholly interior, and placed against the first ; they thus complete one turn of a 



spiral. In quincunxial aestivation (ce. quincuncialis) two of the five pieces are exterior, 



two interior, and one intermediate, one side of the latter being covered by one of the 



outer, and on the other covering one of the inner (fig. 464). This arrangement 



corresponds to that of leaves expressed by J- . To explain this aestivation, which is 



nothing but a depressed spiral with two coils, we must consider the axis of the 



flower as a truncated cone, and draw a spiral line twice round it, from bottom to 



top; then mark off" on this line five equidistant points, so that a sixth point at the 



top of the cone will be immediately above the first ; it is clear that the interspaces 



will equal -f- the circumference of the cone, and the five spaces between the six 



points will constitute */, i.e. twice the circumference; which equals the two turns 



of the spiral traced on the conical axis of the flower. Now substitute for the five 



points five sepals or petals which shall be large enough to overlap ; then depress the 



cone to a plane, and we shall have two exterior leaves (1, 2), a third, at once half 



1 Also called convolute by various botanists. ED. 



