Photo-sensitive "flip-flop" characteristics of the developing Narcissus plant (daffodil phototropism).

The developing Narcissus pseudonarcissus plant (daffodil) is shown to face towards a preferential direction (east, south, west, or north, in that order) before flowering. Said directionality is accomplished by stem bending, a phototropic response mechanism, which is sensitive to partial blocking of the available sunlight from the local environmental. Polar distribution diagrams show that with partial environmental shading from the north, east, south, or west, the developing daffodil plant always excludes facing in that direction, to absorb maximum available sunlight. Stem buckling experiments, equivalent to stem bending, are presented measuring the Euler buckling exponent n =  - 2.1 for daffodil flower stems, in good agreement with theory, r = 0.99. Individual flower stems are capable of generating 2-3 lbf of vertical force, which explains the plants ability to penetrate frozen ground cover. Results from 193 daffodil flower stems are presented, showing that 61.7% face East [95% CI 54-70%], 17.1% face South, 15.0% face West, and only 6.2% face North [95% CI 2-10%], depending strongly on the partial shading effect of the surrounding environment.