150 



ESSENTIALS OF BOTANY 



Study of Unisexual Flowers. — Examine, draw, and describe the 

 unisexual flowers of some of the following dicecious plants and one of 

 the monoecious plants : 



r early meadow rue. 

 Dicecious plants < willow. 



1^ poplar. 



r walnut, oak, chestnut. 



Moncecious plants J.. hickory, alder, beech. 



t. birch, hazel, begonia. 



178. Symmetry of the Flower.- — Most angiosperms have 

 symmetrical flowers. The simplest are those whose parts 

 are arranged as in Figs. 97, 118, having radial symmetry. 



Tig. 101. Bilaterally Symmetrical 



Corolla of Sweet Pea. 



A, side view; B, Iront view dissected 



s, standard; w, w, wings; k, keel. 



A higher type of flower is that which shows bilateral sym- 

 metry, as in Figs. 101, 128. If the drawing of such a 

 flower were folded along the central line, one half of the 

 drawing would cover and correspond with the other half. 

 Some flowers are wholly irregular, showing no sort of 

 symmetry. 



179. The Receptacle. — The parts of the flower are borne 

 on an expansion of the flower-stalk known as the receptacle. 



