THE ESSENTIAL PARTS OF THE FLOWER 83 



diagram (Fig. 35), however, are sufficient to enable students to 

 distinguish epigynous flowers from hypogynous or perigynous 

 ones. 



6. Non-essential parts of the flower; the Perianth. — The 

 calyx and corolla whorls of floral leaves together constitute the 

 perianth of the flower, and as they are not directly concerned in 

 the production of seeds are termed the non-essential parts of the 

 flower. 



When one of the whorls of the perianth is absent as in the 

 mangel, male hop, and anemone, the flower is spoken of as 

 monochlamydeous ; if both calyx and corolla are absent, as in the 

 ash and willow, the flower is naked or achlatnydeous. 



(i) The Calyx. — The Calyx forms a protective covering for the 

 rest of the flower when the latter is still young, and may either 

 fall off' when the flower opens, in which case it is caducous, or 

 remain attached to the receptacle for an indefinite period, when 

 it is described as a persistent calyx. It is usually green but 

 may assume some other colour, in which case it is spoken of as 

 ietaloid. 



A calyx which consists of free separate sepals, as in the butter- 

 cup, is termed polysepalous ; those in which the sepals are united, 

 as in the primrose and pea, are said to be gamosepalous. 



In groundsel, thistle, and other plants belonging to the 

 Compositas, the calyx takes the form of a ring of hair known as a 

 pappus (Fig. 148), which generally develops rapidly after the 

 corolla has faded and acts as a float for the distribution of the 

 seed-case by means of the wind. 



(ii) The Corolla. — This part of the flower is usually of bright 

 colour and serves mainly as an attraction for insects. When 

 the petals forming it are free from each other, as in the buttercup 

 and rose, the corolla \% polypetalous; the term gamopetalous i^ 

 applied to corollas which are composed of united petals, as in 

 the primrose and Canterbury bell. 



7. The essential parts of the flower. — The androecium and 



