STBUCTUBAL BOTANY. 



Trimerous flowers are characteristic of this great group of Plants, 

 while pentamerous flowers commonly distinguish the Exogens. 



66. Deficiencies often occur, rendering the flower incom- 

 plete. Such flowers lack some one or more entire sets of organs. 

 When only one of the floral envelopes, the calyx, exists, the 

 flower is said to be apetalous or monochlamydeous (x^ a M^> a 

 cloak), as in Elm, Phytolacca. These terms are also loosely ap- 

 plied to such plants as Rhubarb, Anemone, Liverwort, where the 

 pieces of the perianth are all similar, although in two or three 

 whorls. When the perianth is wholly wanting, the flower is 

 said to be achlamydeous, or naked, as in Lizard-tail (15). 



is 



16 



\f>, Flower of Saururus (Lizard-tail) achlamydeous. 16. Flower of Fraxinus (Ash). 17, Flower of 

 suiix AVillow), staminate 18, pistillate. 



67. Imperfect flowers are also of frequent occurrence. They 

 are deficient in respect to the essential organs. A sterile or 

 staminate flower (denoted thus $ ) has stamens without pistils. 

 A fertile or pistillate flower ( ? ) has pistils without stamens. 

 Such flowers being counterparts of each other, and both neces- 

 sary to the perfection of the seed, must exist either together 

 upon the same plant or upon separate plants of the same species. 

 In the former case the species is monoecious ( 8 ), as in Oak ; in 



20 ~"V 19 



It, Piitfflate flower of Balm-of-G Head. 20, Staminate. 21, Begonia a, Btaminate; b, pistillate 



