MORPHOLOGY OF LEAVES AND FLOWERS 



605 



Since the work of the flower is to produce seed, and seed forming 

 is due to the co-operation of the stamens and pistils, these are 

 known as the essential organs of the flower. A flower is a perfect 

 flower if it contains both of the essential organs. The simplest 



Fig. 459. 'Essential organs of the flower of the Black Mustard, a, two short 

 stamens ; b, four long stamens. Pistil is enclosed by the stamens ; the 

 filiform body is the filament of the stamen ; the enlarged portion of the 

 stamen is called the anther. 



(After ThomS.) 



flower would have one stamen or one pistil and no corolla or calyx. 

 Imperfect flowers are designated as staminate when they contain 

 stamens, but no pistils; pistillate when they contain pistils but no 

 stamens. The term "bisexual" is applied to the flower which con- 

 tains both stamens and pistils. This is the most common type of 

 flower. 



Fig. 460. Irregular flower of a leguminous plant, dissected so as to show the 



difference in shape and size of petals. 



(After Thomfi.) 



Plants, such as ragweed and corn, which have pistillate and 

 staminate flowers (i. e., pistils and stamens in separate flowers but 

 both kinds of flowers on the same plant) are monoecious (one house- 

 hold) . Such plants as the red campion {Lychnis dioica) , mulberry, 

 willows and poplars, which bear the pistillate flowers on one plant 

 and staminate on .another are dioecious (two households). A plant 



