276 



A TEXTBOOK OF BOTANY 



[On. VI, 3 



Typically they occur a.t the bases of the petals, either as 

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

 spicuously in tne 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. BRAcrsare 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 Bougainvillcea) ; but 

 again they are merely accessory sepal- - 

 likF^ppendages, as in Strawberry, or 

 else they replace the sepals in both jj 

 form and function, as in Sunflower 

 and others of the Composite family. 

 Typically a flower is symmetrically 

 in roTm' around a central axfc, 

 such kinds fel 



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. Alljthat is 



i s the possession of a stamen or a 



istil., A flower which contain^ both is" Maid to be PERFECT, and 

 one which has also petals and sepals is said to hp ^OM 



FIG. 189. A pollen 

 grain germinating on a 

 stigma. (From Sachs.) 



3. THE ACCOMPLISHMENT OF FERTILIZATION BY FLOWERS 

 .t flowers are essential to the produj 



though not everybody knows in what way. 



