SEED-BEARING PLANTS 435 



surface of the stem arise two smooth leaves, with a shiny, 

 but mottled surface, and acute apex. The petioles sheathe 

 the base of a flower-stalk (scape), which also arises from 

 the upper surface of the bulb. At the tip of the flower- 

 stalk is the solitary flower. 



388. Blossoming. Early in the spring the flower-stalk 

 begins to elongate rapidly until it has developed into a 

 long, slender, unbranched stem, the scape, bearing at its 

 tip the flower-bud, raised several inches above the ground, 

 and soon expanding into a flower. During the forma- 

 tion of the flower-bud, in the preceding autumn, the outer 

 surfaces of the floral envelopes grew more rapidly than the 

 inner surface, thus causing the formation of the bud. The 

 opening of the bud is caused largely by the more rapid 

 growth of the inner surfaces of the floral envelopes. 



389. Structure of the Flower. In Erythronium (or any 

 liliaceous plant; cf. Fig. 323) we may recognize all the parts 

 of a complete flower, as follows: 



1. An outer circle of three sepals, together constituting 

 the calyx. 



2. An inner circle of three petals, alternating with the 

 sepals, and together constituting the corolla. The sepals 

 and petals in Erythronium look very much alike, but each 

 petal has a nectary, or gland secreting nectar, at its base. 

 The calyx and corolla together constitute the perianth. 



3. Two inner circles of microsporophylls, the stamens, 

 three in each circle, one opposite each sepal, and one 

 opposite each petal. All the stamens, taken together 

 constitute the androecium* 



*In Erythronium three of the six stamens are frequently noticeably 

 shorter than the other three, and mature their pollen later. This is ex- 

 ceptional in the Lily family, to which Erythronium belongs. 



