Soybean and Bees

Trichomes occur on the pistil and also cover the outer surface of the calyx tube, the bract and
bracteoles. No trichomes are observed on the petals or stamens. The future flower is at first
merely a knob-like primordium in the axil of the bract. The sepals are the first whorl of floral
organs to be initiated. The anterior, abaxial sepal lobe arises first on the abaxial side of the
flower primordium and is followed in rapid succession by the two lateral lobes, and finally,
by the two posterior, adaxial lobes. Very early, the bases of these lobes broaden and fuse, and
later becomes the calyx tube.
All organs of the flower develop rapidly except the petals, which do not elongate much until
the anthers have well-developed microsporangia. The staminal tube, the free stamen, and
the style elongate at the same pace. Thus, the anthers at maturity are clustered around the
stigma. At this time, the petals grow very rapidly, soon surpassing the calyx, stamens, and
pistil to become visible as the flower is in the bloom.
Photo: Decio Luiz Gazzoni
Keel
Wing
Pedicel
Pistil (covered
by the fused
steams)
Calyx
Fused stamens
Figure 12. Structure of a typical Fabaceae flower.
42 SoybeAn and bees