TEE FLOWER 



111 



are of unequal size : such corollas, and all in which the 



petals are not entirely uniform, are 



irregular. 



211. A second important respect in 

 which corollas differ is in the sepa- 

 ration or union of the petals. The 

 trumpet-shaped corolla of the Morn- 

 ing Glory (Fig. 155) furnishes an 

 extreme instance of union, where the 

 original petals are 

 not easily distin- 

 guishable. Fre- 



quently the limh. 



154. Flower of the Violet : 

 below, the parts of 

 the perianth sepa- 

 rated. 



155. Calyx and corolla 

 of Morning Glory. 



or border, is so 

 lobed that the 



number of component parts is evident. 

 Another familiar form is the two- 

 lipped, labiate^ corolla (Fig. 169). 



212. In case the petals remain quite 

 separate, the corolla is said to be poly- 

 petalous ; but if they grow up united when the floral 

 organs are in process of formation, the corolla becomes 

 gamopetalous. When the petals are all wanting, the 

 flower is apetalous. 



213. The calyx presents features very similar to the 

 corolla as regards union of sepals and other modifications. 

 It is usually inferior to the corolla in size and coloration, 

 since its service is chiefly to protect the bud, of which it 

 forms the coat. But in numerous plants the calyx shares 

 with the corolla in another duty. 



214. Functions of the perianth. — The role of the perianth 

 in the natural, history of the flower is chiefly twofold : 

 (1) it protects the developing organs within while the bud 

 is coming to maturity ; and (2) at the time of blooming 

 it aids in the proper distribution of the pollen. Without 

 anticipating the subject of fertilization, it may be said that 

 it is of advantage to plants to secure the dusting of the 

 stigma of each flower by the pollen of some other flower of 



