[The development of pollen grains and formation of pollen tubes in higher plants : V. The division of the generative nucleus in the pollen tube of Tradescantia paludosa].

Fixed pollen tubes of Tradescantia paludosa were investigated cytologically to determine the precise moment of division of the generative nucleus and to measure the length of the pollen tubes at the same time.The exact moment of division of the generative nucleus could be shown to be closely correlated with the length of the pollen tube of Tradescantia. In the majority of the pollen tubes the vegetative nuclei are not yet in the degenerative phase at the time of division of the generative nucleus. In all random samples investigated pollen tubes without nuclei were found. Depending on the random sample the percentage of pollen tubes without nuclei was 11-22%.In the discussion it is pointed out that the data obtained from the cytological investigations show that the findings of the precise moment of division of the generative nucleus agree with earlier published results on the development of pollen grains and formation of pollen tubes. The development of the male gametophyte of the angiosperms is to be divided into a series of stages. The data obtained here from the cyto-morphological studies of pollen tubes of Tradescantia and from cyto- and biochemical investigations of others indicate that the different stages of the pollen grain and the pollen tube can be separated. In the second part of the discussion there is presented an evaluation of the hypothesis that during evolution of the angiosperms species have formed repeatedly, and in most cases probably independently from one another, in which the degenerative phase of the vegetative nucleus begins earlier and earlier during the development of the male gametophyte, or that in some instances DNA replication is either partially or entirely eliminated.