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In our previous papers (Kamizyo and Tanaka 1982a, 1982b), it has been reported that progressive rate of mitosis of the pollen tube generative nucleus varied according to the difference in culture medium. Namely, in Lilium longiflorum, the generative nuclear division was greatly depressed in the artificial medium than in the stigmatic exudate medium. But addition of a suitable concentration of exogenous ATP into the artificial medium has slightly improved the mitotic activity. And furthermore, in both plant species of Lilium longiflorum and Tradescantia paludosa, the mitosis was elated more satisfactorily in the medium supplemented with 10% sucrose than in the medium supplemented with 20% sucrose.It has been well known that artificial storage of pollen grains for a certain time results in erratic germination and destituted elongation of pollen tube in vitro (Johri and Vasil 1961, Linskens 1975). In the course study of pollen tube culture in Tradescantia paludosa, it has been noticed that the ageing of pollen grains affected both viability and mitotic activity of the generative nucleus. This problem will be described here. Materials and methodsThe materials used in this study were taken from the same source as described previously (Kamizyo and Tanaka 1982b), but the methods applied here were slightly modified as follows: A large number of pollen grains collected in the morning of the day of experiments, which will be referred to hereafter as "fresh pollen grains" was allowed to stand for about seven hours at room temperature, which will be referred to as "aged pollen grains". Thus aged pollen grains were sown on the artificial medium at 3p. m., and fixed at 9p. m. and 11p. m., which will be referred to according to the culture duration as "6 hr culture" and "8 hr culture", respectively. The culture medium was supplemented with sucrose of either concentration of 10 or 20%, which will be referred to as "10% sucrose medium" and "20% sucrose medium", respectively. The control cultures of fresh pollen grains were started at 8 a.m., and fixed at 2p. m. and 4p. m. in parallel. Taken procedure will be ab breviated similarly as described in our previous paper, i.e., an expression, "aged pollen grain-10% sucrose medium-6 hr culture", means that pollen grains were sown, after ageing, on the medium supplemented with 10% sucrose at 3p. m. and fixed at 9p. m., and so on.

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