2 1 8 ORGANOGRAPHY. 



rose (Helianthemum), and derives its name from the parts being 

 irregularly contracted into wrinkled folds. The so-called dis- 

 tinctive forms to which the names of induplicate and reduplicate 

 have been given, are merely modifications of the involute and 

 revolute forms of vernation. They should be applied only (as 

 will be presently shown), in describing certain forms of the 

 general arrangement of the component parts of the respective 

 floral envelopes. 



With respect to the relation of the several members of either 

 of the floral envelopes taken as a whole to each other, various 

 forms occur, all of which may be arranged in two divisions ; 

 namely the Circular, and the Imbricated or Spiral. The for- 

 mer includes all those forms in which the component parts 

 of the whorl are placed in a circle, and in nearly the same 

 plane ; and the latter where they are placed at slightly different 

 levels in a more or less spiral manner, and overlap each other. 



1. Circular JEstivation. — We distinguish three forms of this, 

 i.e. the valvate or valvular; induplicative or induplicate; and 

 the reduplicative or reduplicate. The valvate estivation {fig. 

 430), may be seen in the calyx of the Lime, and in Guazuma 

 ulmifolia. In this form the parts are flat or nearly so, and in 

 contact by their margins throughout their whole length, without 



Fig. 430. Fig. 431. Fig. 432. 



Fig. 430. Diagram to illustrate valvate aestivation Fig. 431. Diagram to 



illustrate induplicate aestivation.. Fig. 'k\i2. Diagram to illustrate re- 

 duplicate aestivation. 



any overlapping. This form of aestivation may be generally 

 distinguished, even when the flowers are expanded, by the mar- 

 gins of its component parts being slightly thickened, or at all 

 events not thinner than the rest of the organ ; whereas in all 

 forms of imbricate or spiral aestivation, the overlapping borders 

 are usually thinner, as may be well seen in the sepals of the 

 Geranium. When the component sepals, or petals, instead of 

 being flattened, arc folded inwards at the points where they 

 come in contact {fig. 431), the estivation is induplicative, as in 

 the petals of Guazuma ulmifolia, and in tlie calyx of some 

 species of Clematis. When tlie margins arc turned outwards 

 under the same circumstances {fig. 432), the estivation is re- 



