RECENT ADVANCES IN CONTROL OF FLOWERING AND GROWTH HABIT OF GEOPHYTES
Seasonal thermoperiodism is the most important environmental factor controlling flowering in most bulbous plants. For some geophytes, such as in the autumnal-flowering hysteranthus plants (e.g. Scilla autumnalis, Uriginea meritima) daily thermoperiodism is the environmental factor signaling flowering.
Some geophytes respond in addition to temperature also to photoperiod (e.g. Lilium, Triteleia laxa, Allium ampeloprasum). A special case is the hysteranthous plant Colchicum tunicatum which perceive the photoperiodic signal when the dry bulb lies well below the soil surface.
The size of the apical meristem and not the amount of the carbohydrate reserves in the bulb seems to determine its ability to form flowers. The ethylene-promotion of flowering in Triteleia laxa is not due to enhancement of carbohydrate mobilization, but is correlated with promotion of cell division in the apical meristem and thus the size of the apex dome.