The American Horticultural Magazine 43: 177-180 (1964)
An Effect of Temperature on Development and Differentiation of Rose Flowers
Peter Semeniuk
Crops Research Division, U.S.D.A., Beltsville, Maryland.

Temperature is one of the characteristically cyclical features of the environment. Both rate of growth and the morphogenic development of plants are markedly influenced by the pattern of the temperature cycle to which they are subjected. Temperature influences the growth of plants as much as does any other single factor. This research involves temperature effects in the formation of floral primordia and their eventual form and size.

The effects of five different constant temperature regimes on a seedling of the floribunda rose cultivar 'Ma Perkins' are shown in Figures 1 to 3. Flowers were largest at 62° and 72°F but at 52° the flowers were more intensely colored.

The maximum number of petals was formed at 62°, while at 82° and 92°F the number of petals was reduced to 5, the basic number in wild rose species (Fig. 2). Not only were more petals formed at 62° but at this temperature the petals were more fully expanded.

Fig. 1. Seedling of the floribunda rose cultivar 'Ma Perkins' grown at five different constant temperature regimes.
Fig. 2. Petals and petaloids removed from plants shown in figure 1, showing effects of temperature on their number and size.
Fig. 3. Effect of temperature on length of stamens and pistils of rose cultivar 'Ma Perkins'.
Fig. 4. Sister-seedlings showing effects of temperature on length of stamens and pistils.

Temperature also affected differentiation and development of the reproductive structures of the flower. In the seedling shown in Figure 3 the stamens were fewer and the pistils and filaments were relatively longer at lower temperatures. On the other hand, the number of filaments was greater at the higher temperatures. Figure 4 shows another seedling of 'Ma Perkins' in which the temperature response of the reproductive structures was somewhat different. In this seedling the stamens were long and the pistils short at the lower temperatures.

Thus, temperature causes profound modifications of both the accessory and reproductive parts of the flower. Temperature probably affects the plant mechanisms that control the synthesis and translocation of "hormones," which in turn influence initiation of floral parts, their direction and rate of development. The consequent variations in structure result from a chain of physicochemical reactions initiated by genes but controlled and modified by other genes and the external environment. Temperature effects do not result in any change in or recombination of the genetic factors, and are not transmitted to their descendents. These well-defined morphological characters were affected by the external environment. It is of interest that the lower limit of variability in number of petals imposed by the environment is 5, the basic number in the ancestral species.

Heat, Grtowth, Development, Fertility