86 



OEGAl^OGEAPHT AND GLOSSOLOGY. 



ESTIVATION. 



Estivation {prcefloratio, wstivatio) 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 {m. 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 (cp. induplicativa) when the contiguous parts cohere 

 by a part of their back ; reduplicative {cb. reduplicativa) when by a part of their faces 



460 ffl. Vallate 

 estivation. 



460 S. Valvate 

 induplicative aestivation. 



461. Valvate 

 reduplicative aestivation. 



462. Contorted 

 aestivation. 



463. Imbricate 

 aestivation. 



(fig. 461). 2. Estivation is twisted or contorted^ (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 imhricate. 

 1. In the true imbricate aestivation (ob. imbricativa, fig. 463) 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 (oe. 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 (tig. 464). This arrangement 

 corresponds to that of leaves expressed by f. 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 y, 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 



' Also called convolute by Tarious botauiste. — Ed. 



