Passerina (plant) large enough to cover them. This gives the plants a characteristic plaited or corded appearance. The flowers of some species are borne in terminal spikes, whereas other species bear them in a four-flowered head. Bracts, usually broader than leaves and larger than the flowers, subtend each flower. This is one helpful distinction between specimens of "Passerina" and plants in the genus "Struthiola". The calyx has four sepals, forming a flask-shaped or subcylindrical tube. At the mouth the sepals spread into lobes that are shorter than the tube. There are no petals, but the lobes of the sepals are quite colourfully
Calyx of Held embryonic calyx formation. One characteristic that distinguishes Eph proteins and their receptors from other signaling systems is their ability to transmit information bidirectionally. Forward and reverse signaling in VCN and MNTB cells is essential for the proper number and formation of VCN and ipsilateral MNTB projections in the calyx. Eph proteins also ensure that while axons pass through the ipsilateral MNTB, branching and final termination of these projections only occur in the contralateral MNTB, possibly because the proteins are only targeted towards specific regions on the axons. Overall, there are two ultrastructural changes that occur in the calyx of Held.