170 



FLOWER-BUD. AESTIVATION. 



side is overlapped in like manner by that standing next to it, the 

 aestivation is twisted or contorted, as hi corolla of Althaea rosea (figs. 

 262 p, 264 p). This arrangement is characteristic of the flower-buds 

 of the Malvaceae and Apocynaceae, and it is also seen in the Convolvu- 

 lacea? and some CaryophyDaceae. When the flower expands, the traces 

 of twisting often disappear, but sometimes, as in Apocynaceae, it 

 remains. 



355. In these instances of aestivation, the parts of the verticils are 

 considered as being placed regularly in a circle, and about the same 

 height, and they are included under circular aestivation. But there 

 are other cases in which there is a slight difference of level, and then 

 the true spiral arrangement exhibits itself. This is well seen in the 

 leaves of the calyx of Camellia japonica (fig. 

 265 c), which cover each other partially like 

 tiles on a house. This aestivation is imbricated. 

 At other times, as in the petals of Camelh'a 

 (fig. 265 p), the parts envelop each other com- 

 pletely, so as to become convolute. This is 

 also seen in a transverse section of the calyx 

 of Magnolia grandiflora (fig. 267), where 

 each of the three leaves embraces that within 

 it. When the parts of a whorl are five, as 

 occurs in many Exogens, and the imbrication 

 is such, that there are two parts external, two 

 internal, and a fifth which partially covers one 



of the internal parts by its margin, and is in its turu partially covered 

 by one of the external parts, the aestivation is quincunxial (fig. 266). 

 This quincunx is common in the corolla of Rosaceae. Fig. 266 is a 

 horizontal section of the calyx in the flower-bud of Convolvulus 



sepium, in which the parts are 

 numbered according to their 

 arrangement in the spiral 

 cycle, and the course of the 

 spiral is indicated by a line of 

 points. In fig. 268, a section 

 is given of the bud of Antirr- 

 hinum majus, showing the 

 imbricated spiral arrangement. In this case it will be seen, when 



Fig. 265. Flower-bud of Camellia japonica. c, Imbricated sepals of the calyx, p, Petals with 

 convolute aestivation. 



Fig. 266. Horizontal section of calyx in flower-bud of Convolvulus sepium. Calyx consists 

 of five sepals corresponding to the numbers in the figure, and the line of points indicates the 

 direction of the spiral according to which they are arranged. 



Fig. 267. Arrangement of the three outer leaflets (calyx) in the bud of Magnolia grandiflora, 

 cut transversely ; aestivation convolute. 



Fig. 268. Arrangement of the parts of the calyx in the flower of Frogsmouth (Antirrhinum 

 majtu). The arrangement differs from that in fig. 266, on account of a slight twisting and over- 

 lapping of the parts. 



