Heat, Variation, Flowering and Fertility

Wulff: Triploid Cytology (1959)

Semeniuk: Temperature and Rose fertility (1964)

Moe: Growth, Flowering and fertility in Roses (1988)

Takatsu et al. Temperature and gladiolus pollination (2001)

Delp: Heat in Hybridizing Rhododendrons (1980)

Focke: Digitalis hybrids
Another even more remarkable case is that of certain hybrid foxgloves. Koelreuter, Gaertner, and Focke observed that the hybrids of Digitalis purpurea crossed with D. lutea produced, in addition to a more or less constant intermediate form, a number of forms very different in appearance. Focke observed among the hybrids which grew spontaneously from a cross-fertilized capsule that he had neglected to harvest when ripe, a number of aberrant forms, the most remarkable of them resembling in all particulars a different species (Digitalis tubiflorum). All artificially produced hybrids of these two species have been found to be completely sterile to the pollen of the parent species. The hybrids also occur in nature, in which case they are said to sometimes bear seed.

Kettlewell: Temperature effect on pigment; Heliothis peltigera and Panaxia dominula (1944)

Jones, D.F.: Maize sterility and Heat (1947)

Went: Thermoperiodicity (1948)
Another set of phenomena, which are closely related to vernalization, are the chilling requirements for development of buds of deciduous trees. In most of these plants the buds are dormant for a considerable part of the winter, and can be forced into growth only after having been subjected to freezing temperatures. In some cases the low temperatures may have no other effect than supplying a stimulus, so that a definite time after being subjected to a sudden drop in temperature, irrespective of the duration of this lower temperature, development occurs. The flower buds of the orchid Dendrobium crumenatum offer a clear-cut example (COSTER 1926, KUIJPER 1933). Nine days after a sufficiently rapid drop in temperature (usually associated with a heavy rainfall) the flowers of this orchid open, causing a sudden burst of flowering over a wide area. Some other orchids seem to behave in the same way, and probably other plants as well (gregarious flowering of Coffea liberica). In these cases the flower buds develop gradually up to a certain point, beyond which no growth is possible under the prevailing temperature conditions. The longer the temperature drop is delayed, the more flower buds will have reached the critical size, and the more abundant the flowering is after the temperature drop.

Knight: Effects of high temperature on plants (1819)

Highkin: Temperature-Induced Variability in Peas (1958)

Highkin: Vernalization & Heat Resistance in Peas (1959)


Some plants will survive, even thrive, in high humidity all year long, yet will fail to yield fruit unless they experience a period of dry air.

Collins: Mangos (1903)

Collins: Avocados (1905)