Rates of Growth and Primordial Initiation During Flower Development in Silene at Different Temperatures

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Abstract
The growth of the flower and its constituent parts was measured in Silene coeli-rosa plants, induced at 13, 20 and 27 °C, in order to try and identify those processes which consistently occurred and would therefore be more likely to be essential for flower formation. The increased growth rate of the apical dome just before or about the time of sepal initiation was not maintained in the flower, the growth rate of which was comparable to that of a vegetative apex until all the carpels had been initiated, when it decreased further. The primordia of the same whorl all had similar growth rates so that the relative sizes of the primordia reflected their relative ages since their initiation. The relative growth rate of the stamens was the same (13 and 20 °C) or less (27 °C) than that of the sepals, but the relative growth rate of the petals was lower than either. The growth rate of the flower axis was least at the sepal node and increased both distally and proximally from this region. The plastochron during sepal initiation was shorter than for leaf initiation and tended to be shorter still during initiation of stamens and petals. Increasing temperature increased the rate of primordial initiation but at 27 °C the growth rates of the primordia were lowest although the rates of primordia initiation were highest. The form of the flower, as exemplified by the relative sizes of the primordia at the moment when all carpels had been initiated, was constant despite the differing growth rates and sizes of the primordia on initiation in different temperatures. It is concluded that neither the initiation of the primordia in the flower nor the form of the flower is determined primarily by the relative growth rates of its component parts.