276 



A TEXTBOOK OF BOTANY 



[Ch. VI, 3 



Typically they occur at the bases of the petals, either as 

 glandular swellings, or else as shallow cups, as seen so con- 

 spicuously in the Crown Imperial, where they hold huge 

 glistening drops ; and sometimes they are parts of the re- 

 ceptacle (Fig. 186). Often they are wanting, in which case 

 the nectar is usually secreted from the base of the petals 

 without special glands. Bracts are leaves belonging to 

 the stem below the flower, but often cooperating in the con- 

 struction or function of the flower. Sometimes they consti- 

 tute the conspicuous color-bearing part 

 (as in Poinsettia or BougainviUcea) ; but 

 again they are merely accessory sepal- 

 like appendages, as in Strawberry, or 

 else they replace the sepals in both 

 form and function, as in Sunflower 

 and others of the Composite family. 



Typically a flower is symmetrically 

 radiate in form around a central axis, 

 such kinds being called regular, as 

 with all of those we have thus far 

 mentioned. But many are irregular, 

 with a special tendency to form a two- 

 lipped structure, as in the Mints and 

 Snapdragon (Fig. 187), while this char- 

 acter attains a very extreme development in the Orchids. 

 Its significance will soon be explained. 



Various parts of the flower can be wanting to such a de- 

 gree that pistils only or stamens only remain, thus forming 

 pistillate and staminate flowers respectively. All that is 

 really essential to a flower is the possession of a stamen or a 

 pistil. A flower which contains both is said to be perfect, and 

 one which has also petals and sepals is said to be complete. 



Fig. . 189. — A pollen 

 grain germinating on a 

 stigma. (From Sachs.) 



3. The Accomplishment of Fertilization by Flowers 



Everybody knows that flowers are essential to the produc- 

 tion of seed, though not everybody knows in what way. 



