AESTIVATION, OR PR^EFLORATION. 



135 



cover those within. The most familiar case is that of the petals 

 of Mignonette and the whole genus Reseda. 



255. Valvate or Valvular, when the margins meet squarely in the 

 bud, without any overlapping, like the valves of a dehiscent cap- 

 sule. Familiar examples are afforded by the cahyx of the Linden 

 (Fig. 255) ; also that of the Mallow, Rhamnus, Fuchsia, and the 

 whole of the several natural orders to which these belong. A 

 modification of this, caused by some induplication or involution 

 of the edges of the individual leaves, occurs in most species of 

 Clematis : in Clematis Virginiana, they 



merely project within (yalvate-indupli- 

 cate) ; in Clematis Viticella, they are 

 conspicuously involute (vakate-involute), 

 or valvate with margins involute. Some- 

 times (as in the calyx of certain Malvaceae) the joined edges 

 project outwardly (or are valvate with reduplicate margins) , but 

 only slightly so. 



256. Imbricate or Imbricative is the general name for aestiva- 

 tion (or vernation) with overlapping. The name is taken from 

 the overlapping of tiles or shingles on a roof, so as to break 

 joints or cover edges. It was first applied, by Linmeus, to 

 leaves or scales on a stem, when thickly set and incumbent in sur- 

 cessive ranks or heights, the upper partly covered by those next 

 below. The involucre of an Aster or of the common Sunflower 

 is a typical illustration ; as also the leaves of a Camellia-flower, 

 the sepals as well as the petals ; and the sepals or outer leaves 



260 



of a Flax or a Geranium-flower afford a simpler but similar 

 instance, although, from the parts being nearly of the same size 

 and at the same height, the overlapping is lateral instead of 

 obviously from below. Fig. 258, 259, and the outer part of 

 260, also the inner leafy circle of 255, illustrate in diagram this 

 true and simple imbricative aestivation of a definite number of 



FIG. 25G Valvate-imluplicate flower-leaves (calyx) of Clematis Virginiana, &e. 

 257. Valvate-ijivolute, as in C. Viticella. 



FIG. 258-2GO. Imbricate aestivation : 258, in two whorls of three leaves each (calyx 

 and corolla); 260, same of five leaves in the outer circle, those of the inner circle con- 

 volute; 259, a single set of three imbricated leaves (in the corolla of Magnolia), 

 almost completely encircling each other. 



