Stages in spikelet and flower (floret) development of Zea ear.  Scanning Electron Micrographs (SEM's)

17.  Initiation of first (upper) and second (lower) flowers in spikelets (top of figure) and stamen initiation on slightly older flower (bottom of figure).
18.  Stamen and palea initiation on first (upper) flower. Outer lemma surrounds second (lower) flower.  Outer glume removed.
19.  Gynoecial ridge initiation surrounding the remnant of the gynocecium.  The lower flower is only partially exposed.
20.  Gynoecial ridge forms a complete ring around the remaining synoecium.
21.  Early stage of silk development from the gynoecial ridge in the first (upper) flower.  In second (lower) flower, the two lateral stamens are visible as is the lower palea.  The initiation of the third stamen is indicated.
22.  Early silk development in first (upper) flower and the development of three stamens in second (lower) flower.
23.  Silk development in first (upper) flower with early stages of stylar canal.
24.  Later stage in silk development in first (upper) flower with smaller and retarded second (lower) flower.
25.  Onset of abortion of stamens in first (upper) flower with accompanying gynocium degeneration (↓) in the second (lower) flower.

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Keys to symbols: An3u = anther, 3rd of upper flower; f1 = first (upper) flower; f2 = second (lower) flower; Go = outer glume; GR = gynoecial ridge; Gy = gynocium; Li = inner lemma; Lo = outer lemma; P = palea; Sc = stylar canal; Si = silk; St = stamen (L/U = lower/upper); St3L = stamen of third lower flower. ↓ = degenerating gynoecium

From: Cheng, P.C., Greyson, R.I. and Walden, D.B. (1983). Organ Imitiation and the Development of Unisexual Flowers in the Tassel and Ear of Zea mays.  American Journal of Botany 70(3): 450-462.  Used with permission.