THE PLOKAL ENVELOPES. 125 



1. The valvate. When the sepals or petals fit by their 

 edges, without overlapping each other, as in the mallow. 



2. The imbricated. When the petals or sepals cover each 

 other by a part of their height merely, like the tiles of a roof. 

 The calyx of the Camelia japonica, (Fig. 31,) is a good illus- 

 tration of the imbricated prsefloration. 



3. The contorted. When the petals or sepals exhibit a 

 tortion of their axis, and overlap each other's margins, the 

 whole appearing to be more or less spirally twisted, as in the 

 flowers of the Althsea rosea, (Fig. 31.) 



CHAPTER X. 



THE FLORAL ENVELOPES. 



In a complete flower we find, without the stamens and pistils, 

 two whorls of progressively metamorphosed leaves, the calyx, 

 which is the exterior whorl, and the corolla placed immedi- 

 ately within the calyx. The modified leaves of the flower are 

 brought into close proximity by the non-development of the 

 floral internodes, in order that the sevaral whorls may the 

 more readily communicate with each other ; which immediate 

 communication is necessary to the production of the seed. 

 Let us now examine more particularly the two outermost 

 whorls of floral leaves, designated as the calyx and corolla. 



The calyx, so named from xaXv^ a cup. This forms the 

 outermost whorl of the floral leaves, and consists in its usual 

 state of a leafy green cup more or less divided. The sepals or 

 leaves of the calyx differ but slightly in structure and appear- 

 ance from the ordinary leaves of the stem ; they are for the 



