274 



THE FLOWER. 



cases. 



corolla of Gentians, or outwards, as in that of Campanula (Fig. 443). 

 "When these plaits are laid over one another in a convolute manner, 

 as in the unopened corolla of the Morning-Glory 

 (Fig. 444) and Stramonium (Fig. 447, 448), the 

 aestivation is said to be supervolute. 



503. The direction of the spire or the overlap- 

 ping of parts may be either from left to riglit, or 

 from right to left ; and this direction is generally 

 uniform. In indicating the direction, it is most 

 natural to suppose the observer to stand before 

 the flower-bud. DeCandoUe, indeed, supposes the 

 observer to occupy the centi-e of the flower, which 

 would reverse the direction ; but the former is the 

 pi-evalent view. The direction is frequently re- 

 versed in passing from the calyx to the corolla, 

 sometimes Avith remarkable imiformity ; Avhile 

 again the two occur almost indifferently in many 

 The kind of aistivation, although often the same both in the 

 calyx and corolla, — as in Parnassia (Fig. 381) and Elodea (Fig. 

 375), where both are quincuncially imbricated, — is as frequently 

 different ; and the difference is often characteristic of families or 

 genera. Thus, the calyx is valvate and the corolla couA-olute in 

 all Malvaceae ; the calyx imbricated and the corolla convolute in 

 Hypericum, in the proper Pink tribe, &c. Solitary exceijtions now 

 and then occur in a family. Thus, the corolla in Rosacete is imbri- 

 cated, so far as known, except in Gillenia, where it is convolute. In 

 general it may be said, that the festivation of the corolla is less con- 

 stant than that of the calyx. 



504. The Calyx. In treating of the general structure and diver- 

 sities of the flower, Ave have already noticed the principal modifi- 

 cations of the calyx and corolla, as well as many of the terms era- 

 ployed to designate them ; which need not be here repeated. 



505. The number of sepals that enter into the composition of a 

 calyx is indicated by adjectives formed from the corresjwnding 

 Greek numerals prefixed to the name ; as, disepahus, for a calyx of 

 two sepals ; trisepalous, of three sepals ; tetrasepalous, of four ; pen- 

 tasepalous, of five ; hexasepalous, of six se2:)als ; and so on. A'^ery 

 commonly, however, the Greek word for leaves, phylla, is used in 



FIG 447. Summit Of the unexpanded corolla of Datura meteloides. 448. Transverse sec- 

 tion of tlie same. 



