MORPHOLOGY OF LEAVES AND FLOWERS 609 

 FLORAL ENVELOPES AND THEIR CHARACTERS. 



The sepals and petals constitute tlie two floral envelopes. The 

 envelopes, taken together, are sometimes called the perianth. This 

 is especially true in the lily family where the two envelopes do 

 not differ much in shape and color. Floral envelopes are not es- 

 sential and one or both may be absent. If only one is absent, it is 

 the coroUa, and the flower is apetalous. In the grasses and sedges 

 there is no true perianth but the essential organs are enclosed by 

 chaff-like bracts and glumes. 



Pig. 466 I 



Fig. 466 II 



Fig, 



II. 



466. I. Flower of oats showing the gfass type of floral envelopes. G, 

 empty glume ; Pe, lemna bearing an awn A ; pi, palea ; F. S., sterile flower. 

 Between lemna and palea are pistil and stamens. 



Flower with lemna removed, showing palea and the small bracts (lodloules) 

 at the base of the pistil and stamens. 

 (After Thome.) 



Stamens. — The stamens surround the pistils and their number is 

 various. They may be opposite the petals or alternate with them. 

 In the mustards and buttercups the stamens are inserted on the 

 receptacle. "When they are inserted on the corolla as in the morning- 

 glory, they are epipetalous. Stamens are usually distinct or free 

 from each other. "When they are united by their filaments into one 

 set, as in the mallow family, lupines and lobelia, they are moniai- 

 delphous (one brotherhood). If united into two sets as in clover, 

 they are diadelphous (two brotherhoods). More sets would be 

 designated by tri-, tetra-, etc. 

 39 



