162 



GENERAL BOTANY 



in. the perianth, and many flowers retain for some time the 

 power of opening and closing the calyx and corolla in response 

 to light, temperature, and moisture. They are thus able to 

 serve as a daily protection to the essential organs during the 

 entire flowering period. 



Essential organs. The essential organs of the flower (so named 

 for the reason that they bear the pollen and the ovules, which are 



isccnce line 

 \-Anther sac 



Funiculus^ 



spores 



Boots a 

 FIG. 84. Habit of the mandrake (Podophyllum), with flowers and floral parts 



a, arnandrake plant with a flower; 6, a pistil in section, showing the origin of the 

 ovules on the placenta; c, an ovule, highly magnified to show its parts; d, a stamen, 

 with anther, showing the lines of dehiscence and the pollen ; e, a transverse section 



of the anther 



necessary to the production of seed) are the stamens and the pistil. 

 The stamens in the simple types of flowers arise above the petals, 

 constituting one or more whorls, the number varying in different 

 kinds of flowers. Each stamen is composed of a delicate stalk, 

 or filament, which bears at its apex the anther, composed of two 

 pollen sacs. The pollen grains or spores are developed within 

 the pollen sacs. When the pollen grains are ripe, each anther 

 splits along two lines, called the lines of dehiscence, and the 



