Abstract
1. This paper deals with the effect of low temperature artificially acted upon the pollen formation in the diploid form of Disporum sessile (n=8).
2. The reduction division occured very irregularly at low temperature and the restitution nuclei and dyad cells were often produced.
3. In a large pollen grain produced at low temperature, the diploid number of chromosomes was counted. They showed, considering from their size and shape, the duplication of the haploid set of chromosomes. From such a pollen grain and a normal egg an autotriploid plant may be expected to occur.
4. Thus an experimental basis was given to the assumption that the autotriploid form (2n=24) of this species existing in the nature may have been formed from the diploid form by the abnormal meiosis caused by exceptionally low temperature often coming in warm season when the normal meiosis goes on.
5. In a pollen grain two extra chromosomes were found together with a normal haploid set. The chromosome categories of the formers were identified according to their size and shape. From such a pollen and a normal egg, a double trisomic plant may be produced.
6. In a pollen grain a normal haploid set and an extra chromosome were observed. The latter was recognized to have arisen by the fragmentation of some longer chromosome at its constriction point.
