-ESTIVATION. 



281 



495. The same regularly imbricated arrangement in trimerous 

 flowers gives one exterior, one half interior and half exterior, and 

 one interior member in aestivation, after the order 



of cycles, as is shown in the diagram, Fig. 353, 



both for the calyx and corolla ; which compare 



with Fig. 171, recollecting that the successive 



cycles are superposed in the foliage, while the 



floral circles alternate. Regular imbrication in 



the 4-merous flower gives two outer and two inner 



members in aestivation (as in the calyx of Cruciferous blossoms, 



Fig. 280), on the principle of two decussating pairs of leaves 



(439) ; or it may sometimes be referable to a modification of some 



alternate spiral arrangement. 



496. The degree of overlapping depends upon the breadth of 

 the parts and the state of the bud ; it naturally grows less and 

 less as the bud expands and is ready to open. It is from the full- 

 grown flower-bud, just before anthesis (or the opening of the blos- 

 som), that our diagrams are usually taken ; in which the parts are 

 represented as moderately or slightly overlapping. The same 

 overlapping carried to a greater extent will cause the outer leaf to 

 envelope all the rest, and each succeeding one to envelope those 



within ; as shown in Fig. 354 from one circle 

 of petals of a Magnolia taken in an early state 

 of the bud. Here the mode is just the same as 

 that of Fig. 353. To this, however, has not 

 improperly been applied the name of convo- 

 lute, from its similarity to the convolute verna- 

 tion of the leaves of the branch (257), simi- 

 larly rolled up one within the other. But it is 

 practically inconvenient, and wrong in principle, to designate dif- 

 ferent degrees of the very same mode by distinct names ; further- 

 more, the next general kind of aestivation, when carried to a high 

 degree of overlapping, produces a somewhat similar result ; and 

 moreover, it is to this second mode, whatever be its degree, that 

 the name of convolute is more commonly applied, in recent syste- 

 matic botanical writings. 



497. There are numerous cases of imbricative aestivation, espe- 



FIG. 353. Imbricated aestivation of the calyx and the corolla, in a trimerous flower. 

 FIG. 354. The strongly enveloping imbricative aestivation of the three exterior petals of 

 Magnolia grandiflora. 



24* 



