272 



THE FLOWER. 



ill the Violet, it is probably caused by some slight dislocation that 

 takes place during the early growth of organs in the irregular blos- 

 som. It is not restricted to irregular flowers, however, but occurs 

 as a casual variation, or perhaps more frequent- 

 ly than the quincuncial, in the regular corolla 

 of the Linden (as is shown in Fig. 440). A 

 slight obliquity in the position of the petal No. 

 2, assumed at an early period, would account 

 for the whole anomaly. That this suggests 

 the true explanation is almost demonstrated by 

 the varying aestivation of the corolla of the 

 Linden ; in which the same bunch of blossoms often furnishes in- 

 stances of regular quincuncial imbrication, of the modification here 

 referred to, and of a similar disposition of the fifth petal, throwing 

 one of its edges outwards also. If the first petal were also to par- 

 take of this slight obliquity, the imbricative would be completely 

 converted into what is variously named 



498. The contorted, twisted, or convolutive aestivation (Fig. 439, 

 441, tlie corolla, and 442). In this mode, the leaves of the circle are 

 all, at least apparently, inserted at the same height, and all occupy 

 the same relative position : one edge of each, being directed ob- 

 liquely inwards, is covered by the adjacent leaf on that side, while 

 the other covers the corresponding margin of the contiguous leaf on 

 the other side. Tliis is owing to a torsion or twisting of each member 

 on its axis early in its development ; so that the leaves of the floral 

 verticil, instead of forming arcs of a circle, or sides of a polygon 



having for its centre that of the blossom, severally assume an oblique 

 direction, by which one edge is carried partly inward and the other 

 outward. This contorted cestivation is rare in the calyx, but com- 



FIG. 440. Diagram of the plan and oestivation of the flower of the Linden. 



FTG. 441. Diagram of the imbricated calyx of Wallflower (two outer and two inner sepals), 

 and within the strongly contorted or convolute corolla. 442. Corolla of the latter more open. 

 443. Cross-section of the plaited tube of the corolla of Campanula. 444. Similar section of the 

 plaited and supervolute corolla of Conyolvulus. 



