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. 
