Size of the Chrysanthemum Shoot Apex in Relation to Inflorescence Initiation and Development

The size of the apical dome of Chrysanthemum morifolium Ramat.at the transition to inflorescence initiation in continuouslight (long days) was not systematically influenced by eitherthe temperature or the irradiance under which the plants weregrown. It was generally 0.26 mm in diameter and c. 3.6 x 10^–3mm³ in volume when the first bract was initiated. The dimensionsof the apical dome of plants in short days were only slightlysmaller at this stage. Similarly, each step in the further developmentof the chrysanthemum inflorescence was associated with a narrowrange of apex sizes, indicating that inflorescence initiationand development are closely related to apex size. Chrysanthemum morifolium Ramat, shoot apex, inflorescence initiation     

A Model of Flowering in Chrysanthemum

A mathematical model of flowering in Chrysanthemum morifoliumRamat. is described which may be used to predict quantitiessuch as the number of primordia initiated by the apex, plastochronduration and apical dome mass before, during and after the transformationof the apical meristem from vegetative to reproductive development.The model assumes that primordial initiation is regulated byan inhibitor present in the apical dome. Within each plastochronthe apical dome grows exponentially, and the inhibitor concentrationdeclines through chemical decay and dilution. When the inhibitorconcentration falls to a critical level a new primordium isinitiated. There is instantaneous production of inhibitor, anda decrease in dome mass corresponding to the mass of the newprimordium. The process continues until the apical dome attainsa particular mass when the first bract primordium is produced.Subsequent primordia compete with the apical dome for substrates,and the specific growth rate of the dome declines with successiveplastochrons. Eventually, the net mass of the dome starts todecline until it is entirely consumed in the production of floralprimordia. Chrysanthemum morifoliumRamat, flowering, primordial initiation     

RELATIONS BETWEEN NERVES AND CILIA IN CTENOPHORES

Waves of excitation, visible as ciliary waves, pass along theelongated cells of the ciliated grooves to the comb plates.The frequency of waves is controlled by the loading of the statolithon the balancer cilia, which stand at the head of the grooves.They are primitive mechanoreceptor cilia. A beat of the balancercilia is the initiation of a wave to the comb rows. All ciliain this sensory-conduction-effector line are marked by compartmentinglamellae. This is a distinct system superimposed on others inthe animal, and reasons are given for suggesting that neuroidtransmission in it will prove to be electrical transmission.This system is not anaesthetized by excess Mg⁺⁺. Underwaterripple receptors set off a change in mood in which the animalturns over and swims downwards. There is a variety of modifiedcilia in the apical organ. Other responses such as the inhibitionof the beat, mouth opening, feeding movements, and the protectivewithdrawal of the apical organ, are all co-ordinated by distinctand separate pathways which may prove to be regionally differentiatedparts of one nerve net.