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Telopea Vol. 6(4): 1996 
Because of the spiral phyllotaxy of the petals, and hence the sequential availability 
of antepetalous regions for pre-staminal bulge initiation, the petal and pre-staminal 
bulge sizes are not uniform in early flow'er stages; the first formed petal and pre- 
staminal bulge are significantly larger than those formed last. Initiation of stamen 
primordia is not synchronous, nor even strictly sequential, around the flower; a 
number of stamen primordia are initiated on the oldest pre-staminal bulge well 
before there is any evidence of primordia on the youngest. In terms of the initiation 
of individual stamen primordia, each pre-staminal bulge is operating as a separate 
morphogenetic and phyUotactic unit that is independent of other pre-staminal bulges 
in the flower. 
Another characteristic that defines the pre-staminal bulge as a discrete morphological 
entity that is more than just the collection of its stamens is the fate of the fascicle as 
the flower enlarges. The increase in the circumference of the hypanthium is largely 
the result of expansion in the antesepalous regions; the sepals maintain increase in 
Fig. 22. Diagram illustrating the relationships between PSB formation, stamen initiation and 
hypanthial expansion in flowers with fascicles formed from a pre-staminal bulge, a, petal 
primordia; b, a pre-staminal bulge (PSB) forms on the floral tube directly centripetal to each 
petal; c, the PSB has increased in size and stamen primordia are initiated; d, as more stamen 
primordia are initiated, the PSB increases in size; e, hypanthial expansion in the antesepalous 
region results in the separation of each bundle of stamens. Subsequent extension of the fused 
and free parts of the filaments result in the formation of distinct stamen fascicles. 
