Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Experimental work is carried out using seedlings of the early flowering Chenopodium rubrum system. Flowering can be controlled photoperiodically. Growth and development in terms of plastochron stage, ontogenetic state, at the apex within the differing experimental treatments are examined as are the effects of the light and dark treatments. The plastochron age differs among seedlings of the same chronological age under differing treatments. Effect of the dark is to produce a delay in normal growth and development; this is concommitant with flower induction; the ontogenetic stage of induced apices in the light following the dark is dependent only on the length of the light following the dark and independent of the length of the dark; the apices of both induced and non-induced series show initially a growth spurt and much increased plastochron rate. The same processes and same hormones are required for both apices. The cells within both the induced and non-induced apices show cell enlargement followed by cell division. This involves a "grow and divide" message and with same content--for both apices. The implications for flowering theory are discussed and the concepts of induction and evocation. It is deduced that flowering is conceptually an apical event.;Changes in biochemical activity are consistent with changes in ultrastructure and this was examined in apical cells, primordial leaf and cotyledons. Biochemical status correlates with the phase of the endogenous rhythm of which flowering acts as a marker. The thesis shows that at opposite phases of the rhythm the biochemical status does differ. At those phases of the rhythm when flowering can be induced the apices are biochemically poised. The sensitivity of the seedlings to floral induction changes with changing phase of the rhythm and parallels the endogenous rhythm in ultrastructural and biochemical status. The implications for flowering theory and the concepts of induction and evocation are again discussed.



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