[The development of pollen grains and formation of pollen tubes in higher plants : VI. Pollen grains of Tradescantia with two pollen tubes].

Pollen tube cultures of Tradescantia paludosa, Tradescantia virginiana and the hybrid Hutchinsonii (a cross of Tradescantia virginiana and andersoniana) were placed in vitro under various physiological conditions and analyzed cyto-morphologically in regard to double-tube formation.Depending on the culture conditions and on the plant variety studied there was found for Tradescantia to be a double-tube formation of 13% to 35%. Triple-tube formations as well as branching of the pollen tubes occurred in very rare exceptions. After a 1-2 hour addition of 0,02% colchicin solution to the nutritional medium a drastic reduction of the percentage of double-tubes was determined in the case of Tradescantia virginiana. A double-tube formation of only 6% was observed.In the case of double-tube formations both nuclei always immigrate into the same pollen tube. At the time of immigration the pollen tube with the nuclei is usually the longer of the two.For short growth times of up to 4 hours the averages lengths of both pollen tubes of a double-tube formation is significantly different. The growth of the two pollen tubes does not proceed synchronously. The pollen tube without the migrated nuclei ceases growth early in contrast to the tube containing the nuclei.A comparison of the averages lengths of double-tubes (after the lengths of both pollen tubes were added) with the corresponding values of single-tube pollen grains demonstrates that for experiments 1-5 (cultures under standard conditions and short growth times of up to 4 hours) there is no significant difference between the values. However the values of the double-tube pollen grains are substantially greater than those of the single-tube group in the case of experiment 6-8 (cultures under conditions varying from those of the standard and in some of them growth times longer than 4 hours). The values are significantly different. In experiments 1-5 with two exceptions there is a positive correlation between the averages lengths of the pollen tubes with the immigrated nuclei and those without.The possible causes for the formation of pollen grains with two pollen tubes in vitro are discussed. In the first section the question is debated what the reasons for the asynchronous growth of the two pollen tubes could be. In the second section the hypothesis is presented, that the double-tube formation as found in Tradescantia can be seen from the evolutionary viewpoint as a primitive characteristic. On the other hand the behavior of both nuclei immigrating into only one of the pollen tubes is hypothesized to be an advanced characteristic.