446 BOTANY 



the Angiosperms have for the most part hermaphrodite, cyclic flowers 

 provided with a perianth. The perianth generally consists of two 

 whorls of floral leaves unlike in appearance, and distinguishable as 

 calyx and corolla. The calyx, the outer whorl of the periaDth 

 (Fig. 357, k), functions, as a rule, as a protective organ to the inner 

 parts of the young flower while still in process of development. The 

 leaves of the calyx, or SEPALS, accordingly appear early ; they resemble 

 foliage-leaves in colour and structure, as it would be of no advantage to 

 the young flower, sometimes, on the contrary, a detriment, if they 

 were too conspicuous. 



The COROLLA (Fig. 357, c), on the other hand, is often brightly 

 coloured, so that, even from a distance, it is clearly distinguished from 

 the green foliage. At first concealed in the bud, either enclosed by the 

 calyx or of a green colour, the corolla only attains its full purpose and 

 development when the sexual organs have arrived at maturity and 

 require the co-operation of insects. This condition is indicated by the 

 opening, or ANTHESis, of the flower. The corolla functions not only 

 by means of its colour, but also frequently by its shape and position 

 (cf. p. 283), in the service of pollination. The leaves of the corolla 

 are termed petals ; the mode of their arrangement in the bud 

 (^estivation, see p. 37) is of systematic value. 



While in most flowers of Angiosperms the perianth is double, 

 consisting of a green calyx and a corolla of another colour (hetero- 

 chlamydeous), there are exceptions to this rule. Sometimes the flowers 

 have only a simple perianth (monochlamydeous), or both whorls of a 

 double perianth may be similar (homochlamydeous). In such cases it 

 is customary to speak of a perigone, designating it as calycoid 

 (sepaloid) when, as in the Nettle, it is green or insignificant, corolla- 

 ceous (petaloid) if it is conspicuous and coloured like the simple floral 

 envelope of Clematis or the double one of Colchicwm or Crocus. The 

 separate leaves of the perigone are termed PETALS. 



As an additional exception to the usual structure, the less frequent 

 case may be mentioned in which, as in Aconitum, the calyx is highly 

 coloured while the corolla is inconspicuous. 



The leaves composing the whorls of the perianth may be free or 

 united. In the former case the perianth is spoken of as polyphyllous 

 (also chorisepalous, choripetalous, dialysepalous, dialypetalous) ; in the 

 latter case as gamophyllous (also gamosepalous, gamopetalous, sym- 

 petalous). The upper margin of a whorl of united perianth-leaves is, 

 as a rule, divided into as many teeth or lobes as the number of leaves 

 which enter into its formation. 



The use of the term gamophyllous does not imply that the leaves were origin- 

 ally separate and have subsequently become coherent in the course of their onto- 

 genetic development. On the contrary, the leaves forming such united perianth- 

 whorls have all arisen from one undivided wall-like protuberance of the floral 

 axis. 



