Summary• A putative role for local forces at the surface of the apical meristem for plant organogenesis has been postulated in various studies. To correlate changes in morphogenesis to altered local forces, we followed the geometry of the apical meristem during photoperiodic flower induction in Chenopodium rubrum .• The shape of the apical meristem was determined using cryo-scanning electron microscopy. Cell wall properties on the surface of the dome were visualized using uplight polarization microscopy.• A subtle depression at the summit of the apical dome, typical for the vegetative state, became rounded during the early phase of flower induction. The observed changes were quantified as an increase in the ratio of height to diameter of the dome. In parallel, the properties of cell walls on the surface of the dome changed.• The changes in geometry of the apical meristem were attributed to water movement in the meristem paralleled by a change in cell wall properties at the top of the dome. The results support the hypothesis that local changes in surface tension precede initiation of organ primordia.

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The ultrastructure of generative cells and vegetative cells of Papaver dubium L. pollen was studied with low-temperature scanning electron microscopy (LTSEM). Liquid propane freezing resulted in a very fast fixation. The on-line fracturing and observation of the pollen grains was performed at -130 a C. The specimens were fully hydrated and did not undergo morphological changes during the procedure. Unfractured and cross fractured organelles, generative cells, vegetative nuclei and membranes are visible in three-dimensional images. The LTSEM micrographs show a lobed vegetative nucleus with many nuclear pores and a wrinkled generative cell in longitudinal direction. The vegetative nucleus and the generative cell are situated close to each other but structural connections are not observed.