104 MORPHOLOGY, OR COMPARATIVE ANATOMY. 



is double, that is, a circle of smaller organs, resembling sepals, or a tubu- 

 lar cup, stands outside the proper calyx, forming what is called an 

 epicalyx (fig. 176). The ambiguity in these cases is removed by the 

 existence of a well-developed coloured corolla inside the calyx. 



The epicalyx of Malvaceae, like that of Dipsacese, is perhaps to be 

 regarded as an involucre of bracts. That of Potentilla (fig. 176, B) 

 and allied genera is sometimes supposed to represent confluent lateral 

 lobes or stipular appendages of the sepals. 



Perianth. The terms perianth or periyone are used in a general 

 sense to signify all the floral envelopes, and are specially applied 

 to instances where the distinctions between calyx and corolla are not 

 apparent, e. g. when the sepals and petals are all petaloid, as in the 

 Tulip, &c., and when they are all green and sepaloid, as in the 

 Dock, &c. The words are also applied to the calyx in the Orders 

 where it regularly exists alone, either in a sepaloid or petaloid con- 

 dition, as in Daphne and the Monochlamydeous orders generally. 



^Estivation. The arrangement of the floral envelopes in the bud, 

 the aestivation or pr -defloration, is a subject of great importance in 

 systematic botany, as affording very regular characters in the ma- 

 jority of the natural orders. 



The plans of aestivation given in illustrative works (fig. 177) are taken 

 from horizontal sections of the bud just before it opens; and in cases 

 where the sepals or petals are coherent below, the section is supposed to 

 pass through the free lobes of the limb. 



The aestivation of flower-buds agrees essentially with the verna- 

 tion of leaf-buds (p. 72), especially as regards the folding of the 

 individual organs ; the sepals and petals may be reclinate, condupli- 

 cate, plicate, convolute, involute (a still further rolling-in rendering 

 this induplicate), revolute (in excess becoming reduplicate} ; circinate 

 as in the petals of Hamamelis, and an additional case is found in 

 Poppies and some other flowers, where the petals are irregularly 

 crumpled-up, or corrugate. 



[Collectively the arrangement of the organs is either imbricate, 

 valvate, or open. Imbricate. The varieties of this kind are best seen 

 in whorls of five, which furnish four distinct forms of aestivation, 

 each being cleducible from that which precedes it, by shifting the edge 

 of one petal, as follows : 1. Quincuncial, or the -f plan (fig. 177, A). 

 2. Half-imbricate (B), which only differs from the last in that the 

 4th part overlaps the 2nd. 3. Imbricate proper (C), in which the 

 5th part overlaps the 3rd. 4. Convolute (D), in which the 3rd part; 

 overlaps the first. If convolute petals are twisted, they are called 

 contorted (fig. 177, F). In other words, the axis of a median line clown 

 each petal is erect in the simply convolute, but spiral in the con- 

 torted. 



