THE FLOKAL ENVELOPES. 



105 



Imbricated whorls with four or three parts are usually either 

 imbricate proper or convolute. Whorls with two parts are often 

 equitant (fig. 125), as are the petals of Poppies ; or half-equitant, 

 as the sepals of Poppies, of which each part has one edge overlapping 

 an edge of the other. These two conditions may be regarded as 

 degraded forms of the imbricate proper and convolute respectively. 



A special form of the half-imbricate is seen in the estivation of papi- 

 lionaceous corollas (tig. 177, E), and is named vexillary, from the posterior 

 petal, which is called the vexillum, or " standard." The order of the petals is 

 as follows : The standard is No. 1 ; either keel-petal is No. 2 ; the wing- 

 petal on the opposite side of the flower to the last is No. 3; the other 

 wing No. 4 ; and the remaining keel-petal is No. 5. Thus No. 4 will be 

 seen to overlap No. 2 (see tigs. 191-193, p. 111). 



The aestivation of the Snap-dragon (Antirrhinum majus) is called 

 cochlear, but it is really half-imbricate. 



When the organs are coherent at their margins they may become 

 variously plaited or plicate, the portions sometimes assuming the 

 contorted character, as in the corolla of the Convolvulus (fig. 177, H). 



Fig. 177. 



A 



B 



D 



O/^x y^< */*^ 

 OOO 



Estivation of corollas. 



A. Quincuncial. B. Half-imbricate. C. Imbricate. D. Convolute. (After Gr. Henslow.) E. 

 Vexillary aestivation of the corolla of a Papilionaceous flower. F. Contorted estivation 

 of the corolla of Malva. Gr. Valvate aestivation of the corolla of Viils. H. Plicate 

 aestivation of the corolla of Convolvulus. 



Valvate (estivation. This kind of aestivation occurs when the mar- 

 gins meet but do not overlap (fig. 177, Gr). If the margins of the 

 organs are rolled inwards they are involute or induplicate (fig. 127) ; 

 if, on the other hand, they are rolled outwards, they are called 

 revolute or reduplicate, in both of which cases the rolled borders 

 only are in contact, and not the absolute margins. 



