FLOWER-BUD. ^STIVATIOX. 



169 



with three internal parts, p z, surrounding the essential organs, e, 

 the stamens, and, s, the pistil. 



353. The term perianth then is usually confined to the flowers of 

 Endogens, whatever colour they present, whether green, as in Aspa- 

 ragus, or coloured, as in Tulip. Some use the term perianth as a 

 general one, and restrict the use of perigone to cases where a pistil is 

 present, not applying it to unisexual flowers, in which stamens only 

 are produced. In some plants, as Nymphaea alba (fig. 310), it is not 

 easy to say where the calyx ends, and the corolla begins; as these two 

 whorls pass insensibly into each other. 



354. Flower-bud. To the flower-bud, the name alabastrus (mean- 

 ing rose-bud) is sometimes given, and its period of opening has been 

 called anthesis (oiv9wtf, flower opening), whilst the manner in which 

 the parts are arranged with respect to each other before opening, is 

 the (estivation (cestivus, belonging to summer), or prcefloration (prce, 

 before, andyfos, flower). The latter terms bear the same relation to 

 the flower-bud, that vernation does to the leaf-bud, and distinctive 

 names have also been given to the different arrangements which it 

 exhibits. When the parts of a whorl are placed in an exact circle, 

 and are applied to each other by their edges only, without overlapping 

 or being folded, thus resembling the valves of a seed-vessel, the aesti- 

 vation is valvate, as in Calyx of Guazuma ulmifolia (fig. 261 c). The 

 edges of each of the parts may be turned either inwards or outwards ; 

 in the former case, the aestivation is induplicate, as in corolla of Gua- 

 zuma ulmifolia (fig. 261 p), in the latter reduplicate, as in calyx of 

 Althaea rosea (figs, 262 c, 263 c). When the parts of a single whorl 

 are placed in a circle, but each of them exhibits a torsion of its 

 axis, so that by one of its sides it overlaps its neighbour, whilst its 



Fig. 261. Diagram of calyx, c, and corolla, p, in the bud of Guazuma ulmifolia. ^Estivation 

 of calyx valvate, of petals induplicate. 



Fig. 262. Diagram of calyx, c, and corolla, p, in the flower-bud of Althaea rosea. ^Estivation 

 of calyx reduplicate, of petals contorted or twisted. 



Fig. 263. Flower-bud of Altha;a rosea in a young state, showing calyx, c, still completely 

 enveloping the other parts, and the edges of its divisions touching each other. 



Fig. 264. The same in a more advanced state, where the calycine divisions, c, are separated 

 so as to allow the expansion of the corolla, the petals of which, p, are contorted in aestivation. 



