34 THE FERTILISATION OF FLOWERS. [CHAP. 



-Ceil 



FIG. 38. 



stamens and pistil are the essential organs, because 

 they are necessary for the produc- 

 -Co* tion of seeds. The calyx is 

 usually green ; the corolla gene- 

 rally conspicuous from its bright 

 colours. In some plants the 

 calyx or the corolla is entirely 

 wanting, in which case the floral 

 covering is termed a perianth, as 

 in the Crocus and Lily. 

 The stamens consist of two parts, the filament or 

 stalk (F), and the anther or pollen-case (An). The an- 

 ther is the principal part of the organ, and 

 is filled with a very fine powder like flour. 

 When the anther is ripe, it splits open, 

 and sets free this powder, m pollen as it is 

 called. Examined under the microscope, 

 this pollen is seen to consist of very 

 minute cells filled with protoplasm (fig. 

 40). The pistil occupies the centre of the 

 flower, and is surrounded by the stamens 

 when these are present. It consists of 

 three parts the stigma or surface, the 

 style or stalk, and the ovary at its base. 

 The ovary contains the immature seeds or ovules, 

 which require to be fertilised by the contents of a 

 pollen grain before they can grow into perfect seeds. 

 The style may be absent, and the stigma placed 

 directly on the ovary. The stigma is either sticky, 

 rough, or covered with long hairs, to retain the pollen 

 grains. In some plants the stamens are found in one 

 flower and the pistil in another; they are then termed 



FIG. 39. 



