Generative Cell Division and Sperm Cell Association in the Pollen Grain of Sambucus nigra

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Abstract
Generative cell division in tricellular pollen grains of Sambucus nigra L. (Caprifoliaceae) has been examined with light and electron microscopy. During division the generative cell is located in the centre of the pollen grain, near to the nucleus of a surrounding vegetative cell. Conventional mitosis of the generative cell is followed by cytokinesis through centrifugal cell plate formation. Two sister sperm cells remain in spatial contact with each other and are surrounded, as formerly their progenitor cell was, by the vegetative cell. From the changes of shape of the generative cell during division and of the sperm cells it may be assumed that the space between these cells and the vegetative one contains a labile, non-rigid, wall material. No plastids have been observed in the generative cell and its mitochondria appear to be unequally distributed between the two future sperm cells during division.