In the monocarpic perennial Cynoglossum officinale L.
the probability of flowering is related to the size of the plant.
In previous work it was observed that this relation varies between years.
We hypothesized that variable conditions
during the winter, the period of vernalization, explain this variation.
We collected plants from the field in autumn and placed these under
different simulated winter conditions in
a climate room. In contrast to our hypothesis, the probability of
initiating flowering at a given size was not affected
by: (a) the temperature during the cold period, (b)
the duration of the cold period, or (c) the application of a plant
hormone (GA3) or an inhibitor of gibberellin synthesis (paclobutazol)
during the cold period. Winter cold is not
necessary for floral initiation, and is only required for elongation of
the
inflorescence. It is unlikely that winter
temperature affects the fraction of plants flowering.
Subsequent morphological investigation of flower development in material
collected in the field showed that
large plants had primordial inflorescences well before vernalization,
sometimes as early as August. In plants grown
from seeds under constant conditions in a climate room, the probability
of initiating the inflorescence differed for
plants grown at various temperatures (34·1% at 15°C, 100% at
20°C, and 95% at 25°C). Our results suggest
that environmental conditions in August and September, up to 10 months
before
actual flowering, could affect the fraction of flowering plants.