PATTERN-FORMATION IN THE SUNFLOWER (HELIANTHUS-ANNUUS L) CAPITULUM - BIOPHYSICAL CONSIDERATIONS

In the receptacle of sunflower, new florets originate in an annular ge nerative zone that can be described as ''advancing'' towards its cente r. A floret is first evident as a bump, soon outlined by a parallelogr am of creases. The primordium's bump/crease pattern arises gradually o ver space and time, in a centripetal direction. Kinematic analysis of the receptacle surface has detected a subtle rate of expansion of the surface meristem near the front of the generative zone but negligible or absent towards the center of the empty region of the meristem. It i s proposed that continuous displacement of the centripetally moving ge nerative front, brings about a tendency for the surface to expand. Thi s results is complex physical buckling which not only propagates the o ver-all pattern but also accounts for the complex outline of the new f loret. Then further surface buckling produces a bract and a flower. In the sunflower biophysical phenomena mainly induced by biomechanical f orces of the tunica thus apply to pattern perpetuation per se and the outlining of the floret primordia in the capitulum.