220 ORGANOGRAPHY. 



the parts of a floral whorl are five in number, and these imbri- 

 cated in such a manner that there arc two parts placed on the 

 outside, two inside, and the fifth overlapping one of the internal 

 by one margin, while it is itself overlapped on its other margin 

 by one of the external parts, the estivation is said to be quin- 

 cuncixil {Jig. 435). Familiar examples of this form are afforded 

 by the corolla of the Rose, and the calyx of the Bindweed 

 (^Calystegia sepium). In this form of testivation the spiral arrange- 

 ment of the parts is well seen, and is indicated in the diagram 

 (Jig. 435) by a dotted line. The spiral cycle thus formed, which 

 is the normal one in pentamerous or quinary flowers (those with 

 the parts in fi^'-es), and which occurs in the majority of Dicoty- 

 ledonous plants, corresponds to the f or pentastichous or five- 

 ranked arrangement of leaves. When in aquincuncial arrange- 

 ment the second part of the cycle becomes wholly internal, 

 instead of being external as is ordinarily the case, the regularity 

 of the quincunx is interrupted, and a form of {estivation occurs, 

 to which the name cochlear has been given (^Jig. 436). A fami- 

 liar example is afforded by the Frogsmouth {Antirrhinum majus) 

 and other allied plants. Another modification of imbricate 

 aestivation occurs in the flower-buds of the Pea and other plants 

 allied to it {Jig. 463), where the superior petal or that placed 

 next the axis, called the vexillum, which is generally the largest, 

 is folded over the others which are arranged 

 Fig. 437. face to face (Jig. 437). This form of aestiva- 

 tion is commonly termed vexillary. 



It frequently happens that the calyx and 

 corolla exhibit different forms of restivation. 

 Thus, in Guazuma ulniifolia the calyx is valvate, 

 and the corolla induplicative. In Malvaceous 

 plants the calyx is valvate, or reduplicative, and 

 the corolla contorted. In these examples the 

 different forms of testivation, as exhibited by the 

 Fig. 437. Dia- two floral envclopcs, may be considered to belong 



gram to lUus- ^ ,, i /• .• ^^ • ^i • i 



trate vexillary to the samc class of Kstivatiou, I.e. the circular ; 



and^^'^fwm the ^^^^ instanccs also frequently occur where the 



aiiE or wings, 3 forms in the calyx and corolla arc different, and 



and 5 the ca- bclonir to both classcs. Thus, in the Bindweed 



nna or keel, 4 ,_.,». ^ , , ^ ,' , , , 



the vexillum. ( Calystegia), and other Convolvulacea', the calyx 



is imbricated, and the coroUa contorted. A similar 



arrangement occurs in the Corn Cockle (Lychnis Githago), in 



the St. John's Wort (Hypericum), in the Geranium, and many 



other plants. 



The forms of aestivation above described are always constant 

 in the same individual, and Ircquently throughout entire genera, 

 and even natural orders, hence they are of great importance in 

 systematic botany. For a similar reason they arc also of much 

 value in structural botany, by the assistance they commonly 



