Mechanism of Mitosis in Pollen Tubes

The type of division found in pollen tubes varies with different genera, species, and among pollen tubes of the same culture. Division of the generative nucleus is generally normal in Scilla, Bellevalia, and Zephyranthes, while atypical divisions are frequent in pollen tubes of Tradescantia, Gasteria, and Lilium. When spatial relations are adequate the chromosomes form on an equatorial plate and the anaphase chromosomes pass to their respective poles in unison; but large chromosomes in a narrow pollen tube divide without formation of an equatorial plate, and the daughter chromosomes appear to act as independent units as they pass irregularly to the poles. These divisions are dependent upon the action of the centromeres and a spindle mechanism. Very long spindles are often found in divisions of the generative nucleus, and in Bellevalia they are curved or U-shaped when the division occurs in the pollen grain or in bulges in the pollen tube. The relation of these abnormal divisions is discussed in relation to the mechanics of mitosis.