Narcissus (plant) corona. Floral tubes can range from long and narrow in sections "Apodanthi" and "Jonquilla" to rudimentary ("N. cavanillesii"). Surrounding the floral tube and corona and reflexed (bent back) from the rest of the perianth are the six spreading tepals or floral leaves, in two whorls which may be distally ascending, reflexed (folded back), or lanceolate. Like many monocotyledons, the perianth is homochlamydeous, that is undifferentiated into separate calyx (sepals) and corolla (petals), but rather has six tepals. The three outer tepal segments may be considered sepals, and the three inner segments petals. The transition point between the floral tube and
Calyx of Held the calyx is not only characteristic, but pragmatic in terms of auditory chronological development. As a synapse, the calyx of Held follows a mechanism similar to other synapses. A thorough description can be found under neurotransmission. Calcium influx for the immature calyx of Held is mediated by N-, P/Q-, and R-type calcium channels; however upon maturation only P/Q-type calcium channels become dominant. Upon calcium influx, the immature calyx of Held is highly reactive due to its small calcium buffer ability – this causes the release of glutamate even at low levels of calcium influx. Within the terminal, as with other