THE FLOWER 



253 



Fig. 232. — Unisexual flowers of the Papaw 

 tree : a. staminate, b. i)istillate. 



parts is missing, it is unisexual; if both are present, bisexual. 

 If on a plant bearing unisexual flowers both staminate and 

 pistillate flc^wers are found, 

 e.g., Cocoanut, that plant is 

 called mona'cious (from 

 Greek monos ^onQ, and oikos 

 = house), if, however, stami- 

 nate flowers only are present 

 on one plant of a species, 

 and pistillate ones only on 

 another, as in the Papaw, or 

 the Palmyra Palm, the plant 

 is called dioecious {di meaning two). 



3. Symmetry of Flowers. — if we com- 

 pare several flowers as to the symmetry of 

 their parts, we find two kinds. Some have 

 their parts distributed so regularly round the 

 axis that, divided by any diagonal section, 

 the two halves are equal. Such flowers are 

 radial. They are generally upright or hang 

 down like bells. Examples are the Piose, 

 the Shoeflower, and the Glory Lily. But if 

 we can obtain two similar halves only by one 

 diagonal section, the flower is bilaterally 

 symmetrical or zygomorphic (from Greek zygon ^yok^, and 

 morphe = shape) . Flo- 

 wers of this kind usu- 

 ally open sideways, 

 having their plane of 

 symmetry vertical. 

 This position is advan- 

 tageous for their polli- 

 nation, as the insects 

 which are here the pro- 

 per agents for pollina- ^'^- 234— Zygomorphic flowers. 



tion, come flying from the side. Examples of zj-gomorphic flowers 

 are any of the Papilionacea;, Labiatse, Acanthace* or Orchidacese. 



Fig. 233. — TJie radial 

 flower of Flax. 



